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U.S. District Judge Beryl Howell of the District of Columbia issued a preliminary injunction September 2 directing the Environmental Protection Agency to stop further action on the reclassification and take steps to restore the regulatory status quo that existed before June 12.

EPA’s use of the Congressional Review Act

The dispute stems from EPA’s decision in June to treat four previously granted California preemption waivers as “rules” under the Congressional Review Act (CRA), which allows Congress to overturn qualifying federal regulations using expedited procedures. California argued that Clean Air Act waivers are adjudicatory approvals rather than rules and therefore cannot legally be submitted to Congress for repeal under the statute.

Howell concluded that California had shown a likelihood of succeeding on its claim that EPA’s reclassification was arbitrary and capricious and exceeded the agency’s statutory authority. She ordered EPA to refrain from giving the reclassifications effect and to withdraw or correct its June action.

The four waivers at issue allow California to enforce emissions requirements for cars and small off-road engines. EPA later sought to reclassify two additional waivers covering ocean-going vessels in port and commercial harbor craft, according to the Attorney General’s office.

Implications for California emissions programs

The decision has broader implications for California Air Resources Board programs because federal Clean Air Act waivers have supported California’s ability to adopt emissions standards that are more stringent than federal requirements.

For automakers and fuel suppliers, the litigation affects the regulatory framework governing future vehicle sales and petroleum demand.

Earlier waiver repeals remain in dispute

The ruling does not restore every California vehicle policy challenged by the federal government. Congress previously used the CRA to overturn waivers associated with several California vehicle regulations, including the state’s Advanced Clean Cars II program, which was designed to phase out sales of new gasoline-only passenger vehicles beginning in 2035. California is challenging those earlier congressional actions in separate litigation.

The September 2 decision instead prevents EPA from extending the same strategy to additional California waivers while the current lawsuit proceeds.

That distinction makes the ruling significant beyond the individual emissions programs at issue. If California ultimately prevails, it could restrict the federal government’s ability to use the CRA as an alternative mechanism for dismantling CARB regulations that have already received Clean Air Act waivers.

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The complaint, filed on behalf of the National Highway Traffic Safety Administration (NHTSA), argues that California’s CO2 and ZEV rules function as de facto fuel-economy standards for automakers. Under the federal Energy Policy and Conservation Act (EPCA), which authorizes nationwide Corporate Average Fuel Economy (CAFE) standards, only the federal government can regulate vehicle fuel economy.

In June 2025, Congress revoked California’s vehicle emissions waiver that previously allowed the state to enforce its ZEV mandate. In response, CARB issued emergency regulations in October 2025 to continue enforcing the Advanced Clean Cars II rule, which requires the phase-out of the sale of new gasoline-fueled or diesel-fueled passenger cars and trucks by 2035, and the Heavy-Duty Omnibus rule regulating heavy-duty engines.

The federal government argues that California’s regulations are preempted by EPCA because they are directly related to fuel economy. According to the complaint, “reducing or eliminating tailpipe CO2 emissions from internal combustion automobiles effectively increases fuel economy.”

The complaint states that CARB’s CO2 standards and ZEV mandates “undermine and conflict with NHTSA’s congressionally assigned role in establishing nationwide, uniform vehicle fuel economy standards.” The regulations also “create a patchwork of inconsistent regulation for vehicle and engine manufacturers in an area where Congress imposed a uniform, national approach.”

According to the filing, the regulations “harm the interests of the United States in ensuring American consumers’ access to and choice of reliable, affordable motor vehicle.”

The government also argues that California’s waivers under the Clean Air Act exempt the state from only the Clean Air Act‘s preemption provisions. “Such a waiver has no effect on EPCA,” the complaint states.

CARB has long maintained that its vehicle rules fall within the state’s authority to regulate emissions in order to address air pollution and climate change. State officials have historically argued that the regulations establish emissions standards, not fuel-economy requirements. (For more on California’s auto emissions waiver, see California’s Energy Transition: Part Four—Auto Emissions.)

CARB is currently developing new regulatory proposals in response to Governor Gavin Newsom’s Executive Order N-27-25, issued after Congress revoked California’s emissions waiver. The complaint criticizes those efforts and states that CARB “will continue these unlawful actions unless the Court intervenes.”

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The EPA ruled that an inspection and maintenance program in the State Implementation Plan (SIP) for heavy-duty vehicles that pass through California may violate the Constitution’s Commerce Clause. The EPA stated in its ruling that “extending the regulation to out-of-state vehicles serves the illegitimate objective of outsourcing the costs of attaining the [National Ambient Air Quality Standards] within California to other States and vehicle owners and operators in those States, rather than identifying additional emissions reduction strategies within the traditional ambit of purely in-state sources encompassed within and creditable to the State of California.” The EPA also noted that extending the requirement to vehicles registered in Mexico and Canada could intrude on federal authority over foreign relations and interstate commerce.

“The Trump EPA will never back down from holding California accountable and stopping them from imposing unnecessary regulations on the entire nation,” EPA Administrator Lee Zeldin said in an agency statement. “If California had its way, prices would skyrocket for truckers and businesses across America. Affordable trucks are vital for keeping food and goods moving and prices low for families.”

The California Air Resources Board (CARB) indicated that it will continue enforcing the Clean Truck Check against all vehicles that operate in the state, even if the emissions reductions from out-of-state trucks cannot be credited under the state’s SIP. A CARB official responded that the EPA “has no authority over this program and we will continue to enforce the law to ensure that all trucks operating in California abide by the same rules — even if EPA doesn’t want to give us credit.”

The EPA establishes national ambient air quality standards (NAAQS) under the Clean Air Act for certain air pollutants. States must submit SIPs for the implementation, maintenance, and enforcement of the NAAQS within each state. These plans include emissions limitations and other controls.

California officials have argued that out-of-state and foreign-registered trucks contribute a significant share of NOx and particulate emissions in California and should be subject to the same inspection and compliance requirements as in-state vehicles. In 2023, the California Air Resources Board (CARB) adopted the Heavy-Duty Inspection and Maintenance (I/M) rule to reduce emissions of particulate matter and nitrogen oxide. The rule mandates roadside emissions screening and periodic emissions testing for non-gasoline heavy-duty vehicles operating in California.

The EPA’s decision to reject the out-of-state portion of the rule is a significant federal intervention in the SIP and underscores ongoing tensions between California’s climate policy and the Trump EPA’s regulatory priorities.

Since taking office, the Trump administration has revoked California’s vehicle emissions waivers, which included stringent emissions requirements for heavy-duty vehicles. It has also challenged the state’s Clean Truck Partnership, which aims to advance zero-emission vehicles (ZEVs) for the commercial trucking industry.

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The emergency rule, approved and filed with the Secretary of State on October 2, 2025, is intended to preserve the existing regulatory framework pending ongoing litigation over Congress’s repeal of federal Clean Air Act (CAA) waivers supporting California’s Advanced Clean Cars II (ACC II) and Heavy-Duty Omnibus regulations.

Federal-State Conflict Over Clean Air Act Authority

The dispute centers on California’s longstanding authority under the Clean Air Act to set stricter vehicle emissions standards than federal requirements. That authority was challenged on May 22, 2025, when Congress adopted three resolutions disapproving of EPA waivers underlying California’s clean vehicle regulations.

Separately, the U.S. Department of Justice (DOJ) filed two complaints in August 2025 alleging that California’s emissions rules for light-duty and heavy-duty vehicles are preempted by federal law.

Emergency Rulemaking to Preserve Current Requirements

On September 13, 2025, CARB issued a Notice of Proposed Action for the emergency regulations 2025, allowing it to bypass standard rulemaking procedures. The emergency process allows the agency to avoid typical public notice and comment requirements if it determines that immediate action is needed to prevent harm to public health or welfare. CARB cited risks associated with increased air pollution as justification for expedited action.

The rule is designed to preserve emissions requirements that were in effect—or scheduled to take effect—prior to Congress’s disapproval of the waivers. CARB stated that federal actions and ongoing litigation have created uncertainty over which regulatory standards apply.

Industry Uncertainty and Compliance Risk

The overlapping federal and state actions have complicated compliance for automakers, fleet operators, and logistics companies operating in California and in states that have adopted California’s standards.

Because other states may elect to follow California’s emissions framework under the Clean Air Act, the outcome of the litigation could have nationwide implications for vehicle emissions policy and compliance obligations.

CARB’s emergency rule may stabilize near-term regulatory expectations within California, but it also raises the likelihood of further legal challenges from federal authorities and industry stakeholders.

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The rule, which was implemented in 2023 intended to reduce emissions of particulate matter and oxides of nitrogen, mandates roadside emissions screening and periodic emissions testing for non-gasoline heavy-duty vehicles operating in California. The EPA’s proposal would allow California to implement the HD I/M rule for heavy-duty vehicles registered in the state.

The EPA’s disapproval comes after Congress recently revoked California’s vehicle emissions waivers, which included stringent emissions requirements for heavy-duty vehicles, and the federal government’s recent challenges to the state’s Clean Truck Partnership.

“California was not, and has never been, duly elected by the American people to run our great country,” EPA Administrator Lee Zeldin said. “The state’s power grab knows no bounds. EPA will not allow California to violate federal law, and we will not sit idly by while, in the name of climate change, they raise the cost of living on all Americans who rely on truck drivers and the products they deliver across the country.”

The HD I/M requirement is part of California’s State Implementation Plan (SIP) submitted for approval to the EPA. A SIP, as mandated by the Clean Air Act, includes the regulations used by a state or local air district to implement and maintain the National Ambient Air Quality Standards (NAAQS) as required under the Clean Air Act.

The EPA proposes to disapprove of the state’s application of the HD I/M rule to out-of-state trucks “due to concerns that this requirement violates the U.S. Constitution’s Commerce Clause and this inconsistency with Federal law also violates Section 110 of the Clean Air Act.” Additionally, the EPA states that California’s application of the HD I/M rule to foreign vehicles “appears to ignore the fundamental principal that powers related to foreign affairs are solely vested by the Federal government.”

“California’s approach,” according to the EPA, “appears to be part of a larger strategy to drive out affordable trucks and products based on an extreme climate ideology.”

The proposed partial disapproval and partial approval will be open for public comment for 30 days after publication in the Federal Register.

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CARB issued the report in response to Governor Gavin Newsom’s executive order directing CARB, the California Energy Commission (CEC), Governor’s Office of Business and Economic Development (GO-Biz), California State Transportation Agency (CalSTA), and Department of Consumer Affairs (DCA) to recommend strategies that make clean transportation more affordable, reliable, and accessible.

Newsom issued Executive Order N-27-25 in response to the revocation of California’s vehicle emissions waiver, including the waiver that allows the state to end the sale of new gasoline-fueled or diesel-fueled passenger cars and trucks by 2035. President Donald Trump and Republicans had also discussed at this time the phase-out the federal EV tax credits in negotiations for what became the One Big Beautiful Bill Act (OBBB).

“Clean air efforts are under siege, putting the health of every American at risk,” CARB Chair Liane Randolph, said with release of the report. “California is continuing to fight back and will not give up on cleaner air and better public health — we have a legal and moral obligation.”

Agency Recommendations

The agencies recommended near-term actions around private investment, incentives, infrastructure, fuel pricing, regulations, and procurement.

Private Investment: The report noted the importance of sustaining the state’s Low Carbon Fuel Standard (LCFS) program to ensure continued private investment in the zero emissions vehicle (ZEV) market. This private investment is critical to accelerating ZEV adoption and “moving away from fossil fuels.”

Incentives: The report also discussed the importance of incentives and the need to address both the affordability of vehicles and infrastructure and to support market expansion. This includes:

• Backfill the federal tax credits.

• Support ZEV market deployment incentive and rebate programs.

• Create an education pipeline for good paying jobs.

• Explore options to retain high-occupancy vehicle (HOV) access.

Infrastructure: The report noted that the availability of reliable infrastructure remains one of the largest barriers to ZEV adoption for both private use and commercial deployments. It identified the following actions:

• Collaborative build-out of infrastructure.

• Increase electric vehicle (EV) charger reliability and access.

• Accelerate zero-emission infrastructure build-out.

• Maximize use of existing transportation funding programs to support ZEVs and infrastructure.

Fuel: The report also noted that strategies that reduce the cost of fueling a ZEV will provide long-term support for the ZEV market. It recommended efforts to:

• Explore options to utilize the California Climate Credit to support more affordable ZEV charging.

• Expand regional power markets.

• Leverage private investments to bring down the cost of hydrogen.

• Unlock beneficial Vehicle-Grid Integration (VGI) technology.

Regulations: The agencies recommended two new regulatory programs that will address consumer protection and ensure overburdened communities see the benefits of reduced emissions within their community.

• Advance ZEV consumer assurance measures.

• Advance statewide indirect source rule, which would reduce emissions from mobile sources that frequent indirect sources such as warehouses, ports, airports, and railyards.

Procurement: The report also noted that state has the ability to use its purchasing power as a market participant to increase of ZEV deployments.

• Prioritize use of ZEVs in state procurement.

• Support local government fleet electrification.