The Justice Department sued California on Thursday over the state’s strict emissions regulations imposed on heavy-duty trucks.
The department challenged the California Air Resources Board (CARB) over its “Clean Truck Partnership” that pushes truck manufacturers to phase out internal-combustion engines in favor of “zero emission” engines by 2036. Two separate challenges were filed: One to heavy-duty truck restrictions and another to the guidelines for light-duty vehicles.
“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 the Justice Department’s Environment and Natural Resources Division. “President Donald Trump and Congress have invalidated the Clean Air Act waivers that were the basis for California’s actions. CARB must respect the democratic process and stop enforcing unlawful standards.”
The DOJ is joining a lawsuit brought by several truck manufacturers, including Daimler and Volvo, challenging California over its strident emissions standards.
In its filings, the Justice Department argued that California was illegally trying to supersede federal environmental regulations. California first received approvals from the Biden administration to impose harsher emission standards.
President Donald Trump signed congressional resolutions in June 2025 invalidating the waivers granted by the Biden administration.
“Without these waivers, the Clean Air Act prohibits [the California Air Resources Board] from attempting to enforce those regulations,” the Justice Department said. “Yet, in an affront to the rule of law, [the California Air Resources Board] seeks to circumvent that prohibition by enforcing the preempted emissions standards through the Clean Truck Partnership.”
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The Justice Department argued that California was effectively attempting to “impose a nationwide ban on internal-combustion engines in heavy-duty trucks by 2036” through the regulations promulgated through the “Clean Truck Partnership.”
“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,” the suit said. “CARB continues to threaten truck manufacturers who refuse to comply with its preempted regulations with severe civil sanctions and hostile regulatory treatment.”