• Federal preemption showdown: DOJ sues to halt California truck emissions standards after Congress voided EPA waivers—see how this reshapes 2026 certification and fleet planning.
• Clean Truck Partnership unraveling: Four OEMs sue to void the pact as the FTC closes its antitrust probe with OEM commitments not to enforce it—resetting manufacturer strategy and dealer supply.
• Operational signals to watch: Cummins delays its new X15 diesel amid policy whiplash, while California doubles down via Executive Order N‑27‑25 and CARB rule amendments.

Feds vs. State Showdown in California Truck Emissions Standards

Freight trucks on a California highway. The clash over California truck emissions standards pits state clean-air rules against federal authority.

Federal preemption versus state authority defines the truck-emissions showdown.

In a high-stakes showdown over California’s truck emissions standards, the federal government and California regulators are locked in an increasingly contentious battle. At issue is whether California can enforce its strict emissions rules for heavy-duty trucks – including aggressive zero-emission vehicle (ZEV) mandates – or if federal law will preempt (override) those state standards. This conflict escalated sharply in 2025 and has drawn in truck manufacturers, environmental regulators, and courts across the country.

The outcome could reshape national emissions policy, affect equipment availability, and alter the timeline for adopting electric trucks. Below is a deep dive into the latest developments (especially post-August 15, 2025) and key updates since the original lawsuit in 2023, presented in a factual, impartial manner for industry stakeholders.

For policy dynamics shaping this clash, see our Politics, Laws & Policies reporting.

Legal Battles Escalate (2023–2025) in Emissions Conflict

California has long been a leader in setting stricter vehicle pollution limits under special Environmental Protection Agency (EPA) waivers granted by the Clean Air Act. In 2020, the state adopted pioneering regulations like the Advanced Clean Trucks (ACT) rule (requiring an increasing percentage of new truck sales to be zero-emission) and an Omnibus Low-NOx rule (dramatically cutting diesel truck NOx emissions). By mid-2023, California doubled down with a voluntary deal called the Clean Truck Partnership – an agreement between the California Air Resources Board (CARB) and major truck and engine manufacturers – to push toward zero-emission heavy trucks despite potential legal challenges.

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For more news and updates on the Clean Air Act and related emissions regulations, see our Clean Air Act coverage.

Signed in July 2023 by nine leading OEMs (including Daimler, Volvo, Paccar (Kenworth/Peterbilt), Navistar/International, and engine-maker Cummins), this pact committed manufacturers to comply with California’s truck emissions standards “come what may,” even if federal policies changed. In return, CARB agreed to provide flexibility – aligning some rules with federal 2027 engine standards, granting at least four years lead time for new regulations, and supporting charging/hydrogen infrastructure build-out.

However, that 2023 Clean Truck Partnership soon became a flashpoint. Critics (including other states and trucking groups) argued it effectively bound the entire U.S. industry to California’s strict rules without federal approval, raising questions of federal preemption and even antitrust law. Legal challenges began to mount. In November 2024, the State of Nebraska sued the OEMs and their trade group, alleging the partnership would artificially restrict diesel truck availability and raise prices outside California. Meanwhile, a coalition led by the Western States Trucking Association (WSTA) petitioned California’s Office of Administrative Law to invalidate the Clean Truck Partnership as an “underground regulation” adopted without proper procedure. CARB stood by the agreement, but the stage was set for a multi-front legal battle.

Track evolving truck emissions rules in our Regulations section.

Federal Intervention: Waivers Revoked and Lawsuits Fly

Congress revoked California’s waiver, leaving sweeping truck rules in legal limbo.

The turning point came in 2025 after a change in federal leadership. In January 2025, a new administration under President Donald Trump (returning to office) openly opposed California’s vehicle emissions autonomy. On June 12, 2025, President Trump signed a series of Congressional Review Act joint resolutions nullifying EPA waivers that had allowed California to enforce its Advanced Clean Trucks rule and strict truck NOx standards.

For agency actions and waiver decisions impacting trucking, visit our EPA news hub.

This unprecedented move – enabled by a Republican-controlled Congress – voided California’s legal authority to mandate electric truck sales and more demanding diesel standards, effectively “killing” the state’s zero-emissions rules. Trump declared that the EPA is now barred from approving any similar state-specific emissions waivers in the future, characterizing California’s policies as overreach and “ending the electric vehicle mandate for good”. One resolution specifically blocked California’s Advanced Clean Trucks ZEV sales mandate, and another stopped California’s low-NOx rule from taking effect.

For in-depth coverage of California’s Advanced Clean Trucks (ACT) rule and its impacts, visit our ACT rule news page.

California reacted with defiance. Governor Gavin Newsom condemned the federal rollback as “illegal” and immediately vowed to fight it in court. On June 13, 2025 (just a day after Trump’s signing), Newsom issued an executive order directing CARB to “double down” on zero-emission goals and continue enforcing California’s truck regulations through all means available. He reaffirmed California’s targets of 100% ZEV sales for new medium- and heavy-duty trucks by 2045 (and by 2035 for drayage trucks, alongside similar 2035 targets for cars).

State agencies were instructed to explore new regulations and backfill any lost federal support with state action. “Clean air efforts are under siege… California will not give up on cleaner air,” declared CARB Chair Liane Randolph, citing a “legal and moral obligation” to protect public health. California’s Attorney General and CARB filed suit (in the 9th Circuit and possibly D.C. Circuit) challenging the legality of Congress’s waiver revocation, arguing that the federal government’s action to strip California’s Clean Air Act waivers was unlawful. This counter-lawsuit from California remains pending, setting the stage for a major federalism clash over environmental regulation.

The DOJ is trying to block CARB from enforcing heavy-duty standards now deemed preempted.

Throughout mid-2025, truck makers found themselves caught in the crossfire. CARB officials signaled they still expected manufacturers to comply with state emission rules despite the federal nullification. In late May 2025, CARB issued an advisory warning OEMs that new truck models must meet California standards for certification to be sold in the state. And Governor Newsom’s executive order threatened that any OEM reneging on the Clean Truck Partnership would be blacklisted from state contracts and incentives, with prior regulatory concessions revoked. In other words, California leveraged its market power (about 25% of the U.S. heavy-truck market, including other states following its rules) to insist on continued compliance.

For more news on California’s emissions regulations and CARB’s initiatives, explore our CARB updates.

On the other hand, the U.S. Department of Justice (DOJ), now following Trump’s agenda, told manufacturers the opposite – that California’s truck mandates were preempted and unlawful. The DOJ’s Environment and Natural Resources Division sent cease-and-desist letters to truck OEMs on August 7, 2025, ordering them not to follow California’s “unlawful” standards. The DOJ warned that CARB cannot use a so-called “partnership” to circumvent federal law or delay certifying new vehicles, especially after the waivers were revoked.

Facing these dueling orders, the truck manufacturers broke their public silence. On August 11, 2025, four major OEMs – Daimler Truck North America (Freightliner, Western Star), Volvo Group North America (Volvo, Mack), PACCAR Inc. (Kenworth, Peterbilt), and International Motors (Navistar, owned by VW) – jointly filed a federal lawsuit against CARB, CARB’s executive officer Steven Cliff, and Gov. Newsom. The suit (filed in the U.S. District Court in Sacramento) seeks a declaratory judgment that federal law supersedes California’s truck emissions standards, an injunction to stop California from enforcing any preempted standards, and a ruling that the 2023 Clean Truck Partnership itself is void as an unconstitutional attempt to evade the Clean Air Act.

Stay current on model-year approvals and compliance steps in our Certification resources.

OEMs warn they’re caught in a bind—torn between conflicting federal and state directives.

The OEMs emphasize that they “urgently need clarity” on what emission rules apply for upcoming model years, noting they must plan now for 2026 production and cannot do so under two conflicting regimes. “Plaintiffs are caught in the crossfire,” the complaint states, describing an impossible position where “California demands that OEMs follow preempted laws; the United States says those laws are illegal and orders OEMs to disregard them”. This situation, they argue, is untenable for companies simply trying to build compliant trucks.

The lawsuit points out that without resolution in a matter of weeks, manufacturers won’t know what vehicles they can legally sell and where, particularly since model-year 2026 certification in California (and the dozen “Section 177” states that adopt California’s rules) might be required as early as January 1, 2026.

For additional insights into legal battles shaping the trucking industry, browse our Lawsuits hub.

DOJ Lawsuit and Federal Motions (August 15, 2025)

Just days later, the conflict reached a headline-grabbing peak. On August 15, 2025, the U.S. Department of Justice sued California to halt enforcement of its truck emissions rules. The DOJ filed complaints in two federal courts (Eastern District of California and Northern District of Illinois), intervening in support of the existing lawsuits challenging CARB. Federal lawyers argue that the Clean Air Act preempts California’s “aggressive” truck standards, since Congress has voided the EPA waivers that once authorized them.

The DOJ specifically cited CARB’s Clean Truck Partnership as an unlawful scheme to “ban internal-combustion engines in heavy-duty trucks” despite federal law prohibiting such state action. “Agreement, contract, partnership, mandate – whatever California wants to call it, this unlawful action attempts to undermine federal law,” said Acting Assistant Attorney General Adam Gustafson of DOJ’s ENRD. The official DOJ complaint accuses California of a “stunning act of defiance” by trying to enforce an engine ban through a private agreement. It notes that President Trump’s signing of the joint resolutions in June invalidated the waivers underpinning California’s rules, so under the Clean Air Act, CARB is now prohibited from enforcing those truck standards.

Federal law must prevail, DOJ contends, and it asked the courts to firmly prohibit CARB from any continued enforcement or indirect pressure on OEMs. The DOJ’s move was welcomed by industry as backing the OEMs’ position. Indeed, one of the new DOJ complaints intervenes in the Sacramento OEM lawsuit, and another intervenes in a separate Illinois case (filed in late 2024 by a business coalition) also challenging California’s truck mandates.

Follow nationwide policy debates on required EV adoption in our EV mandates coverage.

California vows to double down on zero-emission mandates despite federal pushback.

These DOJ actions align with President Trump’s broader agenda to “end the electric vehicle mandate” and “level the regulatory playing field”, ensuring one state (even California) cannot dictate national vehicle policy. As DOJ bluntly put it, “The decision whether to ban internal-combustion engines in heavy-duty trucks rests ultimately with the federal government. And it has declined to take such a far-reaching step”. In other words, federal officials argue that California exceeded its authority and that only a uniform federal standard (or Congress) can set such requirements for interstate commerce, like trucking.

To follow the latest federal actions on emissions enforcement, check out our DOJ coverage.

California’s leadership remains unbowed. CARB declined to back down in response to the DOJ suit, with a spokesperson for Governor Newsom reaffirming that the state will “continue to fight back” to defend its climate program. California and allied states (which had adopted the truck rules) are expected to argue in court that the waiver revocations were improper and that California’s unique authority to protect air quality – especially in the face of climate change – should be upheld. These legal battles are poised to continue into 2025 and 2026, potentially even reaching the Supreme Court on the question of state vs. federal power in setting emission standards.

The Clean Truck Partnership Unravels Under Scrutiny

One immediate casualty of this clash is the Clean Truck Partnership itself. What began as a cooperative roadmap between California and manufacturers has now effectively collapsed under legal and competitive pressures. Antitrust concerns emerged in 2025, spurred by an inquiry from the Federal Trade Commission (FTC). After the new administration took office, the FTC launched an investigation, viewing the partnership as a form of industry collusion to restrict production of diesel trucks under the guise of Environmental, Social, and Governance (ESG) goals.

FTC officials noted that four companies controlling 99% of the U.S. heavy-duty truck market had agreed to limit output of specific engines – a red flag for competition. In particular, the FTC identified three problematic aspects of the Clean Truck Partnership:

• “Dead Hand” provision: The OEMs agreed to abide by CARB’s ZEV mandates even if those regulations were later invalidated, creating a private backdoor enforcement mechanism. This meant the companies would still stop selling most diesel models and produce “zero-emission” engines only, effectively self-imposing a ban on internal-combustion trucks because a now-voided state rule had once required it. Regulators warned this could eliminate competition and consumer choice without any government oversight.
• Mutual enforcement: Nothing in the deal prevented one manufacturer from holding a competitor to the agreement’s terms. In theory, an OEM could sue or pressure a rival for selling trucks that violated the partnership (for example, by exceeding a cap on diesel engine sales). This raised fears of collusion, where competitors police each other to maintain a united front, limiting traditional trucks.
• Lack of accountability: The agreement was made outside the normal political process, locking in long-term market rules that neither voters nor elected officials could easily modify. If California’s government or the federal government changed course (as indeed happened), the private pact could undermine democratic oversight, effectively letting regulators and companies “freeze” a policy in place. FTC Chair Andrew Ferguson criticized it as companies “agreeing to eliminate competition and reduce output” under an ESG pretext.

Dive deeper into market shifts and equipment trends in our heavy‑duty trucks coverage.

The Clean Truck Partnership unraveled under antitrust pressure and legal risk.

By August 2025, under mounting pressure, the truck OEMs formally backed away from the Clean Truck Partnership. On August 10, just before their lawsuit, Daimler, Volvo, Paccar, and International each signed letters to the FTC disclaiming the partnership’s enforceability. They pledged never to enforce its terms against each other, and never again to enter into any similar agreement that fixes production or emissions limits in concert with a state regulator. The Truck & Engine Manufacturers Association (EMA), the industry trade group that helped broker the deal, likewise agreed not to negotiate such pacts in the future.

Satisfied with these commitments, the FTC announced on August 12, 2025, that it would close its antitrust investigation. “The Commission’s swift action will put the Clean Truck Partnership squarely in the rearview mirror,” said an FTC Bureau of Competition official, who called CARB’s private agreement a “troubling regulatory gambit” that posed a significant threat to American trucking.

For more analysis of antitrust issues affecting trucking, read more on Antitrust.

The unwinding of the partnership was a relief to some and a blow to others. Nebraska’s Attorney General, who had sued over the pact, hailed the outcome as a victory, ensuring diesel truck availability “will be dictated by market forces, not unelected bureaucrats in another state”. The day the OEMs filed their lawsuit against CARB, Nebraska dropped its case, declaring that the industry “under assault by California” had been set free. On the other hand, environmental advocates slammed the manufacturers for a “cynical reversal.”

They note that the same companies had negotiated the Clean Truck Partnership to get regulatory certainty and flexibility, yet now chose to “blow up that agreement” when political winds shifted. A senior clean-trucks advocate with the NRDC called it “bad faith… plain and simple,” questioning if these OEMs are genuinely committed to delivering clean vehicles. CARB officials also view the OEM retreat as a betrayal of trust, since California had granted concessions (like delaying specific NOx rules and offering compliance flexibility) in exchange for the OEMs’ ZEV commitments.

Amid this turmoil, even engine-maker Cummins Inc. (which was a signatory to the 2023 agreement but not part of the OEMs’ lawsuit) is feeling the effects of uncertainty. In August 2025, Cummins announced a delay in the rollout of its new heavy-duty X15 diesel engine, citing the murky regulatory outlook. Without clarity on emissions requirements and certification – federal standards vs. California’s now-preempted standards – the company opted to pause introducing the engine to avoid compliance risks. This concrete impact underscores how the regulatory whiplash is unsettling product planning across the industry.

For updates on the latest developments from Cummins, visit our Cummins news.

Impacts on Fleets, Manufacturers, and the Supply Chain

Fleets face compliance fragmentation if mid-’20s mandates vary across Section 177 states.

Beyond the courtroom, this federal-state clash over emissions rules carries wide-ranging implications for the trucking industry and supply chain. Fleet operators and truck dealers, in particular, have been caught in a limbo as policies see-saw. Many trucking fleets had begun investing in zero-emission trucks (battery-electric or hydrogen fuel-cell) and charging infrastructure to comply with California’s timeline. Billions of dollars in state and private investment have poured into pilot programs, vehicle orders, and infrastructure. For instance, California approved a $2.9 billion plan in late 2022 to build out ZEV charging and hydrogen fueling stations for trucks and buses. The state’s overall climate initiative allocated over $10 billion to ZEV programs, including incentives for electric trucks.

For more news and updates on the shift to electric trucks and zero-emission fleets, explore our Electric Trucks section.

Major truck makers also spent heavily to develop new electric models and comply with CARB’s now-jeopardized rules. If California’s standards are ultimately struck down, some of these investments (in factories, technology, and training) could be delayed or face lower utilization. Conversely, if California prevails, manufacturers will be pressed to accelerate zero-emission offerings nationwide to meet the strict sales quotas. The regulatory uncertainty is itself costly: companies are hesitant to make long-term bets when the rules of the game could change with a court decision or election.

Will California’s truck emissions standards still take effect?

As of late 2025, California’s zero-emission truck mandate and other emissions rules are in legal limbo. Formally, because of Congress’s action, the EPA waivers for those rules are revoked, meaning under the Clean Air Act, the California standards are not legally enforceable unless the courts reinstate the waivers or otherwise rule in California’s favor. However, California is pushing forward de facto via the Clean Truck Partnership (for now) and its market power.

CARB has continued to approve new regulations and amendments to advance its climate goals. For example, on July 24, 2025, CARB adopted amendments to its Advanced Clean Fleets rule (which will require public and drayage fleets to buy zero-emission trucks on a schedule) and referenced the Clean Truck Partnership commitments even after the federal rollback. Moreover, CARB has hinted it could use state-level enforcement tools like withholding certification of new diesel models that don’t meet its standards, effectively barring their sale in California. Governor Newsom’s administration is also exploring new state regulations or legislation to achieve similar ends if the original rules are permanently blocked.

Read ongoing updates on CARB’s fleet rule at Advanced Clean Fleets.

Infrastructure, cost, and range still limit zero-emission truck adoption across many operations.

For example, California could enact fleet purchase requirements, tighter in-use emissions rules, or other indirect methods to cut truck emissions. Nonetheless, until the legal questions are resolved, manufacturers and fleets face ambiguity. They must plan for compliance with two divergent scenarios: one where California’s zero-emission sales requirements for trucks ramp up starting in 2024 (as originally scheduled), and one where those requirements are nullified and replaced by more modest federal standards. This ambiguity has essentially frozen certain decisions – as seen with Cummins delaying its engine launch – and could slow the pace of zero-emission truck deployments in the near term.

In the other states that had opted into California’s program (such as Oregon, Washington, New Jersey, New York, Massachusetts, and others), the effect is similar. More than half a dozen states have formally adopted California’s Advanced Clean Trucks rule to spur local EV truck adoption. Without a valid California rule (due to waiver revocation), those states’ adoption under Section 177 of the Clean Air Act is also void, potentially leaving a patchwork of standards. Some states may wait on the court outcomes, while others could pursue their own legislation to enforce truck emission cuts, raising the specter of regulatory fragmentation.

Truck manufacturers could be forced to juggle different rules if, say, a state like New York finds a way to keep ZEV sales mandates alive while others fall away. This scenario is precisely what many in the industry feared: a fragmented market that complicates product planning and distribution. It’s no surprise that the American Trucking Associations (ATA) and other trade groups favor one national standard. ATA’s president Chris Spear applauded the June 2025 federal actions, saying it brings the nation “one step closer” to realistic and achievable single nationwide emissions standards rather than a patchwork.

How are trucking fleets and manufacturers adapting?

Fleets have been watching these legal proceedings closely and hedging their bets. Large trucking companies that operate in California (and the states following its lead) had begun ordering electric trucks, both to comply with future mandates and to meet corporate sustainability goals. With mandates in question, some fleets might slow-roll further EV orders until there’s certainty – especially given the cost and infrastructure challenges cited by many operators. The Owner-Operator Independent Drivers Association (OOIDA), representing small trucking businesses, has long argued that mandating electric rigs too soon would be impractical.

After Trump’s June 2025 intervention, OOIDA called it a “big win” for truckers, saying “electric trucks just aren’t a realistic option right now – they’re too expensive, the charging infrastructure isn’t there”. Indeed, concerns about charging infrastructure, grid capacity, vehicle range, and cost remain barriers to rapid EV truck adoption. If California’s timeline is delayed, fleets may choose to continue running diesel equipment longer or invest in cleaner diesel technology (like newer low-NOx engines) as a bridge.

For state programs, incentives, and rule updates, explore our California policy & freight news.

On the manufacturing side, companies are proceeding with caution but not abandoning electrification. Daimler, Volvo, Paccar, and other OEMs have publicly reiterated commitments to reducing emissions – even as they fight the legal mandate, they invest in electric and hydrogen models for the future market. In fact, by dismantling the Clean Truck Partnership, the OEMs have freed themselves to lobby for more flexible regulations. They are likely to push the EPA and Congress for a single national program that gradually increases zero-emission truck sales, still, with timelines they consider achievable and aligned with infrastructure rollout.

A negotiated national standard could replace patchwork rules with predictable targets.

Industry players are emphasizing the need for substantial government investment in charging infrastructure and power grid upgrades if any ZEV mandate is to succeed. Many fleet operators and truck makers suggest a pragmatic approach: continuing to innovate in zero-emission technology while also deploying interim solutions like renewable fuels, hybrid systems, and low-NOx engines to cut emissions in the near term without an outright EV mandate.

Meanwhile, California is leveraging incentives and market mechanisms to keep the transition moving. The state still offers significant purchase vouchers and credits for zero-emission trucks, and regional air quality agencies provide grants for electric truck charging depots. If anything, the clash with the feds has led California to propose even more aggressive state investments to ensure its climate goals aren’t derailed.

In August 2025, California agencies recommended steps like backfilling lost federal EV funding, streamlining permits for charging stations, and even restoring perks like HOV lane access for ZEVs to spur adoption. These measures, however, require stable financing and political support within the state – at a time when California is also grappling with budget constraints (some planned climate investments have been trimmed due to revenue shortfalls).

From a supply chain perspective, the uncertainty over emissions rules could affect equipment availability and resale values. If California’s rules were enforced, it would have effectively created a two-tier market where compliant ZEV trucks are required in certain states. Fleets operating nationally might have had to maintain separate equipment pools (electric trucks for California/177 states, diesel for elsewhere) or avoid sending non-compliant trucks into California. That scenario appears to be on hold for now, much to the relief of nationwide carriers. “We cannot allow one state’s regulations to disrupt our entire nation’s supply chain,” said a truck driver at the June White House event celebrating the waiver repeal.

Stay updated on the latest trends and ripple effects across the supply chain, and explore our Supply Chain reporting.

Truck availability should improve across all states if manufacturers are not forced to cap diesel engine production in the next few years. Indeed, Nebraska’s Attorney General argued that dissolving the Clean Truck Partnership ensures an ample diesel truck supply and helps keep transport costs in check for consumers. On the other hand, if California ultimately prevails and reimposes its ZEV mandate a few years down the road, there could be a mad scramble for compliance – OEMs might need to scale up ZEV manufacturing rapidly. Fleets could face shorter timelines to replace diesel trucks, potentially straining production capacity and leading to equipment shortages or higher prices in the late 2020s.

Outlook: High-Stakes Emissions Clash Continues

A negotiated national standard could replace patchwork rules with predictable targets.

This federal vs. California emissions clash remains highly dynamic. As of late August 2025, legal proceedings are underway on multiple fronts. California is fighting to restore its authority, the Trump administration is using every tool (legislation, lawsuits, FTC action) to block what it calls California’s “EV mandate,” and truck makers are seeking judicial clarity to avoid being squeezed between conflicting laws. The following key milestones will likely be court rulings on the OEMs’ lawsuit and California’s challenge to the waiver revocation.

A federal court could issue a preliminary injunction or declaratory judgment in the coming months that tilts the balance – for example, upholding federal preemption (which would officially pause California’s enforcement) or conversely, siding with California (which could allow the state to continue its programs while litigation continues).

Industry stakeholders should prepare for continued uncertainty. Regulatory fragmentation is a real risk if states pursue divergent paths pending a final resolution. Fleets and manufacturers may need contingency plans for different regulatory outcomes in 2026 and beyond. In the best case, this clash could prod the federal government and California toward a compromise – perhaps a single national standard that is ambitious but with more realistic phase-in schedules, giving industry time to adapt. In the worst case, protracted litigation and political back-and-forth could delay progress on cutting emissions, leaving everyone in limbo and undermining investment by creating a yo-yo effect in policy.

One thing is clear: both sides frame the stakes as enormous. California officials argue that urgent climate and air quality goals depend on pressing forward with zero-emission trucks (especially in communities suffering from diesel pollution). The federal administration and much of the trucking industry argue that economic stability and technological feasibility hang in the balance, warning against rushing unproven solutions that could disrupt commerce. This clash of priorities – environmental leadership vs. national uniformity and market practicality – makes the outcome hard to predict.

For now, industry insiders should track the legal developments closely and continue engaging with policymakers. Fleet compliance planning should remain flexible, focusing on building EV capacity where it makes sense (e.g., for local and regional operations where incentives and infrastructure are in place) while advocating for clear, achievable regulatory goals. Manufacturers will likely continue advancing zero-emission technologies (to stay competitive globally and meet inevitable future standards), but also need to support customers with efficient diesel options during the transition.

Keep up with vehicle and infrastructure progress in our zero‑emission trucking initiatives.

In summary, the California truck emissions standards showdown is far from over. The period since the original 2023 agreement has seen dramatic twists: a cooperative pact turned into a courtroom brawl, congressional intervention undoing environmental rules, and a flood of legal and administrative actions on both sides. This controversy is ripe for further analysis as it tests the limits of state authority, the direction of U.S. climate policy, and the trucking industry’s readiness for change.

Stakeholders should brace for a rocky road ahead – but also recognize that, once the dust settles, the resolution (whether via court decision or policy compromise) will set a critical precedent for how the U.S. balances clean air ambitions with economic and technological realities in the transportation sector.

Key Developments — California Truck Emissions Standards (2023–2025)

• 2023 – Clean Truck Partnership signed: CARB and leading manufacturers agree to support ZEV truck adoption with regulatory flexibilities and lead‑time commitments.
• Dec. 18, 2024 – EPA waiver granted (Low‑NOx): EPA approves California’s omnibus heavy‑duty NOx rule, setting the stage for stricter HD standards before the 2025 reversals.
• Nov. 19, 2024 – Nebraska antitrust suit: Nebraska sues OEMs and EMA over alleged collusion tied to the Clean Truck Partnership.
• June 12, 2025 – Waivers revoked: Congress passes, and President Trump signs, CRA resolutions voiding California waivers (ACC II, ACT, Low‑NOx).
• June 12, 2025 – California “doubles down”: Governor Newsom issues EO N‑27‑25, directing agencies to craft next‑generation clean‑vehicle actions.
• July 24, 2025 – CARB amendments: CARB adopts amendments referencing Clean Truck Partnership commitments to keep ZEV momentum despite federal rollbacks.
• Aug. 6–7, 2025 – Cummins delay: Cummins postpones launch of its EPA‑2027 X15 diesel to late 2026, citing regulatory uncertainty and market conditions.
• Aug. 11–12, 2025 – OEM lawsuit filed: Daimler Truck North America, Volvo Group NA, PACCAR and Navistar sue CARB/Newsom in E.D. Cal., seeking relief from preempted state standards and the CTP.
• Aug. 12, 2025 – FTC closes probe: FTC ends its antitrust investigation after OEM/EMA commitments; Commission warns the CTP posed “obvious” competition risks.
• Aug. 15, 2025 – DOJ lawsuits: DOJ sues to stop California from enforcing truck standards via the CTP, arguing Clean Air Act preemption after waiver repeal.
• Aug. 18–19, 2025 – DOJ interventions: DOJ moves to intervene in two related cases challenging CARB’s enforcement of preempted HD standards.
• Aug. 25, 2025 – EPA proposes SIP disapproval: EPA proposes to disapprove California’s heavy‑duty inspection/maintenance requirement as applied to out‑of‑state vehicles (Clean Truck Check), citing legal conflicts.
• Market footprint & timing pressure: OEMs state they need near‑term clarity on MY2026 certification for California and opt‑in Section 177 states representing ~25% of U.S. HD registrations.
• California counters in court: California and allied states sue over the federal rollback on June 12, seeking to restore waiver authority.

Related Tank Transport reporting

• California emission regulations — facts & impacts (ACT/waivers overview)
• California tightening diesel rules (pre‑ACF context and timelines)
• California’s long‑term diesel phase‑out and ZEV goals (ACF/ACT linkage)
• Electric Class 8 pilots and fleet results (Tesla Semi & operations)
• Electric yard trucks and drayage transitions (uptime, ROI, incentives)
• Heavy‑duty charging corridor build‑out (infrastructure readiness)
• Clean Air Act enforcement in the diesel aftermarket (penalties & compliance)
• ACT credit uncertainty affecting OEM sales (Daimler Oregon update)
• Hydrogen vs. battery‑electric — duty‑cycle fit analysis
• Hydrogen fuel‑cell deployment learnings (Benore case)
• Managing diesel costs amid policy uncertainty (strategies & levers)
• OEM manufacturing expansion for electric trucks (capacity & timing)

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Authoritative External References for the California Truck Emissions Standards Showdown

• Justice Department press release on the lawsuit to end enforcement of California truck emissions standards (Aug. 15, 2025): Justice Department – California truck standards case
• EPA overview of California waiver and authorization process under the Clean Air Act: EPA – California waivers & authorizations
• GAO legal analysis on whether EPA California waiver decisions are subject to the Congressional Review Act (CRA): GAO – Observations on EPA waiver/CRA applicability
• Statutory text establishing federal preemption and state limits: 42 U.S.C. § 7543 (Clean Air Act §209)
• CARB program page detailing manufacturer ZEV sales requirements: CARB – Advanced Clean Trucks (ACT)
• CARB program page outlining fleet purchase schedules and compliance pathways: CARB – Advanced Clean Fleets (ACF)
• CARB’s heavy‑duty inspection & maintenance program hub: CARB – Clean Truck Check (HD I/M)
• Governor’s executive order reaffirming state zero‑emission goals and directing next steps (June 2025): State of California – Executive Order N‑27‑25 (PDF)
• EPA announcement proposing to disapprove California’s HD I/M requirement as applied to out‑of‑state vehicles (Aug. 25, 2025): EPA – Proposed action on Clean Truck Check scope
• FTC press release closing its antitrust inquiry into the Clean Truck Partnership with manufacturer commitments (Aug. 12, 2025): FTC – Clean Truck Partnership resolution
• Nebraska Attorney General statement on resolution of the Clean Truck Partnership litigation (Aug. 11, 2025): Nebraska AG – Clean Truck Partnership case update
• CARB certification guidance for on‑road heavy‑duty engines and vehicles: CARB – On‑Road Heavy‑Duty Certification Program