In a dramatic escalation of the ongoing emissions regulation dispute, four major truck manufacturers, including industry leaders Daimler and Volvo, have initiated legal action against the state of California. The lawsuit, filed this Monday, contends that the state's enforcement of certain emissions standards—previously invalidated by the Trump Administration—places unfair legal burdens on manufacturers.

The core of the lawsuit, lodged in the US Court for the Eastern District of California, seeks a declaratory judgment against California's Clean Truck Partnership (CTP) and related Manufacturers Advisory Correspondence. The manufacturers argue these initiatives act as "underground regulations," violating California Government Code § 11340.5(a). The complaint highlights the untenable position of the Original Equipment Manufacturers (OEMs), stating, "Plaintiffs are caught in the crossfire: California demands that OEMs follow preempted laws; the United States maintains such laws are illegal and orders OEMs to disregard them."

The CTP, a collaborative agreement with California’s Clean Air Resources Board, pushes for adherence to state vehicle emission standards and the adoption of zero-emission technology. This is in spite of any federal challenges to California's authority under the Clean Air Act (CAA), from which the state typically secures waivers due to its unique environmental challenges. However, the landscape shifted dramatically with recent federal legislative changes under the Trump Administration.

In mid-2025, Congress passed the Congressional Review Act, incorporating measures specifically designed to curb California’s regulatory powers over vehicle emissions. This legislation effectively repealed Section 209 of the CAA and nullified existing waivers, a move President Trump described as rescuing "the US auto industry from destruction."

California's response was swift and defiant. Governor Gavin Newsom criticized the federal government's actions as detrimental to both the state's environmental goals and America's position in the global market. Meanwhile, the state proceeded to enforce its CTP, leading to further complications as the Department of Justice issued a cease-and-desist order to the truck manufacturers in early August, demanding an end to their compliance with the CTP.

The ongoing legal battles reflect a significant clash between federal and state powers, with substantial implications for environmental policy and the automotive industry. As the lawsuit progresses, the truck manufacturers seek clarity and relief from what they describe as contradictory regulatory demands that have left them "irreparably harmed by this uncertainty." The outcome of this case could set important precedents for how vehicle emissions are regulated across the United States, especially in states with unique environmental challenges like California.