US DOJ sues California over enforcement of HD truck emission regulations
19 August 2025
The US Department of Justice (DOJ) has filed two complaints in federal courts against the California Air Resources Board (CARB) regarding the state’s enforcement of preempted emissions standards through its Clean Truck Partnership with heavy-duty (HD) truck and engine manufacturers.
The Clean Truck Partnership is an agreement between manufacturers and CARB, where CARB committed to relaxing their Omnibus Low NOx emission requirements and providing longer lead time for new emission regulations. In exchange, truck manufacturers committed to meeting CARB’s zero-emission and criteria pollutant regulations in the state “regardless of any attempts by other entities to challenge California’s authority.”
As the federal waivers for California to implement the CARB emission regulations have been withdrawn, truck manufacturers—including Daimler Truck, International, Paccar, and Volvo—have filed a law suit against CARB over the enforcement of Clean Truck Partnership emission requirements. This law suit is now supported by the DOJ. In its court filings, the DOJ states:
In defiance of federal law, the State of California is attempting to use its own vehicle and engine emissions standards through a so-called “Clean Truck Partnership” to ban internal-combustion engines in heavy-duty trucks, notwithstanding duly enacted federal statutes specifically providing that those regulatory standards are preempted. The Clean Truck Partnership is California’s attempt to enforce three sets of stringent emissions standards adopted by the California Air Resources Board (“CARB”): the Omnibus’ Low NOx (“Omnibus”) rule, the Advanced Clean Trucks (“ACT”) rule, and the Advanced Clean Fleets (“ACF”) rule. Individually or collectively, these emission standards effectively impose a nationwide ban on internal-combustion engines in heavy-duty trucks by 2036.
In June, US President Trump signed into law congressional resolutions, invalidating EPA’s preemption waivers for the CARB Omnibus Low NOx regulation and the ACT rule (as well as the Advanced Clean Cars II regulation). Earlier, CARB withdrew its EPA waiver request for the ACF rule.
Without these waivers, the Clean Air Act prohibits CARB from attempting to enforce those regulations, the DOJ emphasized. Yet, CARB seeks to circumvent that prohibition by enforcing the preempted emissions standards through the Clean Truck Partnership. The Justice Department’s Environment and Natural Resources Division (ENRD) filed the complaints with motions to intervene in pending cases in the Eastern District of California and Northern District of Illinois. The EPA is a co-plaintiff in the filings.
“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 ENRD. “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.”
In related actions, ENRD moved to dismiss as moot two sets of cases in the US Court of Appeals for the Ninth Circuit where industry groups had challenged EPA’s preemption waivers for cars. Those cases—the DOJ said—are now moot because Congress’s joint resolutions nullified the controversial preemption waivers.
Source: US DOJ