EPA to Challenge "Illegal" California Heavy-Duty Truck Inspection Rules

EPA Proposes to Deny California’s Heavy-Duty Truck Rules

EPA Proposal Targets California’s Plan

The U.S. Environmental Protection Agency (EPA) announced a proposal to deny portions of California’s Heavy-Duty (HD) Inspection and Maintenance (I/M) program. California’s plan would have required all heavy-duty trucks driving in the state to meet inspection and maintenance standards, including those registered outside California or outside the United States.

The EPA said it is proposing to disapprove these requirements. The agency explained that California’s approach may conflict with federal law. It also warned that the plan may violate the U.S. Constitution’s Commerce Clause.

EPA Raises Concerns About Federal Law

EPA officials said the proposal rests on two main issues. The first is the Constitution’s Commerce Clause, which gives Congress control over interstate trade. The agency said California’s rules could create unfair burdens on trucking companies operating across state lines.

The second issue involves the Clean Air Act. Section 110 of the Act requires state implementation plans to be consistent with federal law. The EPA said California’s effort to regulate foreign-registered vehicles could conflict with powers that belong only to the federal government, such as foreign affairs.

If the disapproval is finalized, California would not be able to enforce this part of its program.

EPA Review of California’s Inspection Program

California’s plan was designed to cover every heavy-duty truck that operates within its borders. That included vehicles from other states and other countries. The state aimed to create a single standard across all trucks traveling in California.

The EPA said states do have authority under the Clean Air Act to take steps that improve air quality. But the agency also said that authority is limited. According to the EPA, California may have gone too far by applying its program to trucks registered outside its jurisdiction.

Public Comment Period Open

The EPA will publish its proposal in the Federal Register. Once published, the public will have 30 days to provide comments. Trucking companies, industry groups, state agencies, and individuals will all have the opportunity to respond.

The agency said it will review every comment before issuing a final decision. The agency may revise the proposal or confirm the denial as written.

Action Follows Federal Court Cases

The EPA’s action comes after new lawsuits were filed earlier this year. The U.S. Department of Justice brought two cases against the California Air Resources Board (CARB). These cases challenge the state’s agreements with truck and engine makers under the “Clean Truck Partnership.”

Federal officials said the agreements attempted to enforce standards not approved at the federal level. The cases are still in progress, and the outcomes could influence how future rules are shaped.

EPA and Congressional Action on Waivers

In addition to court cases, Congress has acted on California’s waivers. In February 2025, the EPA sent three California vehicle waivers to Congress. These included Advanced Clean Cars II, Advanced Clean Trucks, and Heavy-Duty Engine Omnibus NOx standards.

In June 2025, both chambers of Congress passed resolutions disapproving the waivers under the Congressional Review Act (CRA). The resolutions were then signed into law.

The votes canceled California’s ability to enforce the three programs. Supporters of the disapproval said national consistency was necessary. They argued that allowing one state to set vehicle standards for the nation would create unnecessary burdens.

EPA Notes Impact on Trucking and Supply Chains

If finalized, the EPA’s disapproval of California’s I/M program would affect interstate trucking. Long-haul carriers often travel across several states and into Canada or Mexico. Under California’s plan, these carriers would have faced additional inspection rules whenever entering the state.

The agency said these requirements could have increased costs for drivers and trucking companies. The agency also warned that the program might have disrupted the flow of goods, creating new challenges for supply chains.

EPA officials said national consistency in vehicle standards helps the trucking industry avoid conflicts and manage costs. This, they said, is one reason why the agency is questioning California’s approach.

EPA Highlights Ongoing Debate Over Standards

California has a long history of pursuing stricter rules than those set at the federal level. For years, the state has applied for Clean Air Act waivers to adopt rules that go beyond national standards. The state has argued that its unique air quality challenges justify such measures.

The agency has now taken a different stance. The agency said it aims to limit California’s ability to set rules that affect trucks beyond its borders. Recent moves, including the proposed disapproval of the I/M program and reversal of earlier waivers, reflect this shift.

What Happens Next

The proposal to deny California’s Heavy-Duty I/M program highlights an ongoing debate over authority between states and the federal government. The agency has opened a public comment period and will review all feedback before making a final decision.

At the same time, lawsuits, congressional actions, and agency reviews are all moving forward. Together, these efforts could shape how truck emission standards are set across the United States in the future.