California Emissions Standards Lawsuit: DOJ Suits and Waivers

The California emissions standards lawsuits are not a single case but four parallel legal fights, all active in mid-2026 and none yet decided on the merits. A coalition of 11 states led by California is suing the federal government over Congress’s nullification of the state’s Clean Air Act waivers. The Department of Justice has filed two separate suits against the California Air Resources Board — one targeting truck rules, one targeting passenger-vehicle CO2 and zero-emission mandates under a different federal statute. And the Supreme Court has cleared the way for fuel producers to challenge California’s original electric-vehicle waiver on the merits in the D.C. Circuit. One related fight, over the Advanced Clean Fleets rule, has been settled.

What California Was Doing

Under Section 209(b) of the Clean Air Act, California can ask the EPA for a waiver to enforce its own vehicle emissions rules if they are at least as strict as federal standards and address “compelling and extraordinary conditions.”¹ The EPA has granted more than 75 such waivers over 50 years and had never revoked one until the first Trump administration did so in 2019.² Under Section 177, other states can adopt California’s rules; as of 2025, 17 states plus Washington, D.C. had done so for light-duty vehicles, and 10 for heavy-duty.³

Three programs sit at the center of the current disputes:

Advanced Clean Cars II (ACC II), requiring 100% zero-emission new light-duty vehicle sales in California by 2035.
Advanced Clean Trucks (ACT), requiring manufacturers to sell rising percentages of zero-emission trucks.
The Omnibus Low NOx rule for heavy-duty engines.

EPA granted waivers for all three between 2023 and January 2025.¹

Congress Nullified the Waivers, and California Sued

In spring 2025, Congress used the Congressional Review Act — a tool normally aimed at federal agency rules — to strike down the three waivers. H.J. Res. 87, 88, and 89 targeted the ACT, ACC II, and Omnibus Low NOx waivers.⁴⁵

The process was contested. Both the Government Accountability Office and the Senate Parliamentarian had determined that Clean Air Act waivers are not “rules” subject to the CRA. The Senate majority voted 51-46 to set those determinations aside.² Once signed, the resolutions declared the waivers had “no force or effect” and barred the EPA from issuing future rules “substantially the same” without new congressional authorization.⁶

California sued the same day. Attorney General Rob Bonta, Governor Gavin Newsom, and CARB filed State of California v. United States, No. 4:25-cv-04966, in the Northern District of California, naming the United States, the EPA, Administrator Lee Zeldin, and President Trump as defendants.⁴ Colorado, Delaware, Massachusetts, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont, and Washington joined.⁶

The states argue that the CRA covers only agency rules and that Clean Air Act waivers are adjudicatory orders, citing the GAO and Parliamentarian conclusions. They also raise the Tenth Amendment, structural federalism, separation of powers, and the Article II Take Care Clause, and contend the EPA reclassified its waiver decisions as rules to create a “pretextual basis” for the CRA’s use.⁶ They ask the court to declare the resolutions unconstitutional and without effect on state emissions programs.⁴

The Trump administration responded that California cannot use the courts to “override the will of Congress”⁷ and filed a motion to dismiss the amended complaint on November 17, 2025.⁴ In December 2025, the court, Judge Haywood S. Gilliam Jr. presiding, denied motions to intervene from Texas, various trade groups, and the Zero Emission Transportation Association.⁸ The motion to dismiss remains pending.

CARB Kept Enforcing, Under a Different Rule

With its newer waivers nullified, CARB fell back on its older Advanced Clean Cars I waiver from 2013, which it argues remained in force and outside the CRA resolutions’ reach. In September 2025 the board adopted emergency vehicle emissions regulations effective October 2, 2025, codifying CO2 standards and ZEV sales mandates.⁹¹⁰ CARB proposed readopting the rule through June 30, 2026, while pursuing permanent rulemaking. That continued enforcement triggered the federal government’s next two lawsuits.

The DOJ’s Two Direct Suits Against CARB

August 2025: The Truck Emissions Suit

On August 15, 2025, the DOJ and EPA sued CARB in the Eastern District of California and the Northern District of Illinois over continued enforcement of heavy-duty truck standards after Congress had voided those waivers in June.¹¹ The vehicle for that continued enforcement, according to the complaints, is the Clean Truck Partnership, a June 2023 agreement between CARB and the Truck and Engine Manufacturers Association covering companies that represent more than 90% of California’s truck market, including Daimler Truck North America, Paccar, Volvo Group North America, and Cummins.¹² Under the agreement, manufacturers committed to comply with the Omnibus Low NOx and Advanced Clean Trucks regulations regardless of the outcome of legal challenges, and not to support litigation against them.¹³ DOJ called the partnership a “regulatory mechanism by which CARB attempts to enforce preempted California emissions standards.”

Four manufacturers — Daimler, Paccar, International Motors, and Volvo Trucks North America — filed their own suit against CARB on August 11, 2025, arguing the partnership is moot because the underlying waivers have been revoked and the state standards are preempted.¹²

March 2026: The EPCA Suit

On March 12, 2026, DOJ, acting for NHTSA, filed a new suit against CARB and its executive officer in the Eastern District of California, Case No. 26-at-00450.¹⁴ This one rests on the Energy Policy and Conservation Act rather than the Clean Air Act. The federal argument: EPCA designates NHTSA as the exclusive regulator of vehicle fuel economy, and California’s CO2 standards and ZEV mandates “relate to fuel economy standards” and are therefore preempted regardless of any Clean Air Act waiver.¹⁵

The complaint targets CARB’s fleetwide CO2 cap of 131 grams per mile for passenger cars and the ZEV sales mandate that starts at 22% in 2025 and climbs to 100% by 2035. It also asks the court to block CARB’s in-development Advanced Clean Cars III regulations before they are finalized.¹⁵ DOJ seeks a declaratory judgment that the regulations are unlawful and a permanent injunction against their enforcement.¹⁴ The EPCA theory matters because it would strip California’s authority even if the state wins the CRA constitutional case.

Diamond Alternative Energy: The Fuel Producers’ Case

Separate from the federal-versus-state litigation, fossil fuel producers have been challenging California’s Advanced Clean Cars I waiver — the same 2013 waiver CARB is now leaning on. In Diamond Alternative Energy, LLC v. Environmental Protection Agency, No. 24-7, the American Fuel and Petrochemical Manufacturers, Diamond Alternative Energy (a renewable diesel company), and Valero Renewable Fuels Company argued California’s regulations suppress demand for liquid fuels by pushing automakers toward EVs. They estimated more than $1 billion in annual injury, projected to exceed $10 billion by 2030, and argued the Clean Air Act’s waiver provision was designed for local air quality, not global climate change.¹⁶¹⁷

The D.C. Circuit dismissed the case for lack of standing, finding the producers could not show that invalidating the regulations would actually cause automakers to build more gasoline vehicles given “surging consumer demand” for EVs.¹⁸¹⁶¹⁹

The ruling decided only standing. The D.C. Circuit will now consider on the merits, for the first time, whether the EPA lawfully approved California’s original Advanced Clean Cars waiver.²⁰ The ACC I standards remain in effect while that review proceeds.

The One Piece That Has Settled: Advanced Clean Fleets

CARB’s Advanced Clean Fleets rule, adopted in April 2023, would have required truck fleets in California to phase in zero-emission vehicles toward 100% zero-emission sales in medium- and heavy-duty categories by 2036 and full fleet conversion by 2045. A coalition of 17 states led by Nebraska Attorney General Mike Hilgers challenged it in the Eastern District of California.²¹

CARB settled. It agreed to present a proposal to its board to repeal the “high-priority fleet” and “drayage fleet” requirements, with an initial statement of reasons published by September 1, 2025, a public hearing before October 31, 2025, and any board-approved repeal submitted to California’s Office of Administrative Law by August 31, 2026.²² CARB also agreed to stop enforcing those requirements retroactively to November 1, 2023, and conceded that the 2036 sales mandate cannot be enforced without an EPA waiver — which it acknowledged is unlikely under the current administration.²¹ The case is held in abeyance pending completion of the rulemaking.

What to Watch

Four things are pending. The federal government’s motion to dismiss the states’ CRA challenge in the Northern District of California, before Judge Gilliam. The DOJ’s EPCA suit in the Eastern District, which offers a preemption theory independent of the waiver question. The DOJ’s truck suit and the manufacturers’ parallel challenge to the Clean Truck Partnership. And the D.C. Circuit’s first merits review of the Advanced Clean Cars I waiver following Diamond Alternative Energy. CARB’s own docket lists dozens of additional active cases touching emissions standards for passenger vehicles, trucks, locomotives, forklifts, and harbor craft.²³ The common question across all of them is whether California keeps the regulatory autonomy it has exercised since before the modern Clean Air Act, or whether the federal government holds exclusive control over vehicle emissions policy.

1
U.S. Environmental Protection Agency. Vehicle Emissions California Waivers and Authorizations
2
Office of the Attorney General, State of California. California Will Not Waver Defending Itself From Federal Overreach
3
Environmental Defense Fund. Green Groups File Amicus Brief in Support of California Clean Car and Truck Standards
4
Clearinghouse. State of California v. United States
5
DieselNet. DOJ Sues California Over ZEV Mandates
6
State Impact Center. California v. United States Amended Complaint
7
Law360. Trump Admin Says Calif Emissions Waiver Fight Is DOA
8
Climate Case Chart. California and Other States Challenged Congressional Review Act Disapproval of Clean Air Act Waivers
9
California Air Resources Board. Emergency Vehicle Emissions Regulations Readoption Notice
10
U.S. Department of Transportation. CARB EPCA Complaint
11
U.S. Department of Justice. Justice Department Sues California to End Enforcement of Unlawful Emissions Standards for Trucks
12
CCJ Digital. Truck Makers Sue CARB, Challenge Legality of Clean Truck Partnership
13
California Air Resources Board. Final Agreement Between CARB and EMA
14
U.S. Department of Justice. President Trump’s Justice Department, Transportation Department Sue to Stop California’s Illegal Emissions Standards
15
Jurist. US Government Sues California Over Electric Vehicle Mandate
16
Supreme Court of the United States. Diamond Alternative Energy, LLC v. Environmental Protection Agency
17
Cornell Law Institute. Diamond Alternative Energy, LLC v. Environmental Protection Agency
18
New York Times. Supreme Court Rules Fuel Producers Have Standing to Challenge California Electric Vehicle Standards
19
SCOTUSblog. Diamond Alternative Energy LLC v. Environmental Protection Agency
20
Environmental Defense Fund. Supreme Court Ruling Does Not Address Merits of California Vehicle Standards
21
Trucking Info. California to Officially Repeal Advanced Clean Fleets Rules
22
FreightWaves. California Deal With 16 States Would End Key Parts of Advanced Clean Fleets Rule
23
California Air Resources Board. CARB Current Litigation