The U.S. Environmental Protection Agency (EPA) issued a final rule January 27, 2026 disapproving of California’s inspection and maintenance requirements on out-of-state trucks passing through the state. The EPA approved California’s Heavy-Duty (HD) Inspection and Maintenance (I/M) Regulation only as it applies to in-state registered vehicles. The EPA proposed its disapproval of the so-called Clean Truck Check rule on out-of-state vehicles in August 2025.
The EPA ruled that an inspection and maintenance program in the State Implementation Plan (SIP) for heavy-duty vehicles that pass through California may violate the Constitution’s Commerce Clause. The EPA stated in its ruling that “extending the regulation to out-of-state vehicles serves the illegitimate objective of outsourcing the costs of attaining the [National Ambient Air Quality Standards] within California to other States and vehicle owners and operators in those States, rather than identifying additional emissions reduction strategies within the traditional ambit of purely in-state sources encompassed within and creditable to the State of California.” The EPA also noted that extending the requirement to vehicles registered in Mexico and Canada could intrude on federal authority over foreign relations and interstate commerce.
“The Trump EPA will never back down from holding California accountable and stopping them from imposing unnecessary regulations on the entire nation,” EPA Administrator Lee Zeldin said in an agency statement. “If California had its way, prices would skyrocket for truckers and businesses across America. Affordable trucks are vital for keeping food and goods moving and prices low for families.”
The California Air Resources Board (CARB) indicated that it will continue enforcing the Clean Truck Check against all vehicles that operate in the state, even if the emissions reductions from out-of-state trucks cannot be credited under the state’s SIP. A CARB official responded that the EPA “has no authority over this program and we will continue to enforce the law to ensure that all trucks operating in California abide by the same rules — even if EPA doesn’t want to give us credit.”
The EPA establishes national ambient air quality standards (NAAQS) under the Clean Air Act for certain air pollutants. States must submit SIPs for the implementation, maintenance, and enforcement of the NAAQS within each state. These plans include emissions limitations and other controls.
California officials have argued that out-of-state and foreign-registered trucks contribute a significant share of NOx and particulate emissions in California and should be subject to the same inspection and compliance requirements as in-state vehicles. In 2023, the California Air Resources Board (CARB) adopted the Heavy-Duty Inspection and Maintenance (I/M) rule to reduce emissions of particulate matter and nitrogen oxide. The rule mandates roadside emissions screening and periodic emissions testing for non-gasoline heavy-duty vehicles operating in California.
The EPA’s decision to reject the out-of-state portion of the rule is a significant federal intervention in the SIP and underscores ongoing tensions between California’s climate policy and the Trump EPA’s regulatory priorities.
Since taking office, the Trump administration has revoked California’s vehicle emissions waivers, which included stringent emissions requirements for heavy-duty vehicles. It has also challenged the state’s Clean Truck Partnership, which aims to advance zero-emission vehicles (ZEVs) for the commercial trucking industry.