Four major truck manufacturers, including Daimler and Volvo, filed a lawsuit against the state of California on Monday, aiming to block authorities from enforcing emissions standards voided by President Donald Trump’s administration.

The suit requested the US Court for the Eastern District of California to issue a declaratory judgment against the state, arguing California’s Clean Truck Partnership (CTP) and a Manufacturers Advisory Correspondence affirming the CTP are “underground regulations” in violation of California Government Code § 11340.5(a).  Plaintiffs also asserted that California should be enjoined from enforcing any disputed vehicle emission standards without a waiver of preemption from the Environmental Protection Agency (EPA). The complaint argued:

Plaintiffs are caught in the crossfire: California demands that OEMs (Original Equipment Manufacturers) follow preempted laws; the United States maintains such laws are illegal and orders OEMs to disregard them… As a result, the OEMs are subject to two sovereigns whose regulatory requirements are irreconcilable and who are openly hostile to one another… Accordingly, Plaintiff OEMs file this lawsuit to clarify their legal obligations under federal and state law and to enjoin California from enforcing standards preempted by federal law… The OEMs are in an impossible position… Plaintiff OEMs have been irreparably harmed by this uncertainty.

The manufacturers are part of the CTP, an agreement with California’s Clean Air Resources Board that requires truck manufacturers to meet state vehicle emission standards and adopt zero-emission technology, regardless of any challenges to California’s authority under the federal Clean Air Act (CAA). In exchange, the truck companies have received flexibility and support in meeting those standards.

Part of the CAA prohibits states from setting their own vehicle emissions standards without a federal waiver.  However, Section 209 of the CAA allowed California, with its specific environmental needs, to seek waivers from the EPA.  The Biden Administration had granted such a waiver for truck emissions.

In July, Congress passed the Congressional Review Act, which Trump signed. The act incorporated the Stop California from Advancing Regulatory Burden Act of 2025, repealing Section 209 and nullifying existing waivers.

“We officially rescue the US auto industry from destruction by terminating the California electric vehicle mandate once and for all,” Trump said when signing the bill.

In response, California leaders have criticized the legislative measures. “Trump’s all-out assault on California continues,” California Governor Gavin Newsom said. “And this time he’s destroying our clean air and America’s global competitiveness in the process.”

In May, California issued a Manufacturers Advisory Correspondence, which affirmed the CTP and the expected vehicle emission standards.  On June 12, California joined 10 other states in suing the Trump Administration, challenging the legality of the Congressional Review Act.  While the case is pending, California has continued to try to enforce the CTP.

On August 7, Adam Gustafson, the acting assistant attorney general for the Department of Justice’s Environment and Natural Resources Division, sent a cease-and-desist letter to the manufacturers, in which the companies were ordered to end CTP compliance.