Late last week, the US Senate voted to revoke 3 of California’s emissions waivers, which allowed the state to enact more stringent vehicle-emissions standards than the federal standard. The House had already passed the resolutions several weeks prior, in a set of bipartisan votes. Given that President Donald Trump is widely expected to sign the resolutions, California’s unique role in expanding climate regulations could be coming to an end.

Background: California’s emissions waivers have their roots in the Air Quality Act of 1967, which generally barred US states from adopting their own emissions standards but provided an exemption for California due to its smog issues at the time. The Air Quality Act was later amended to become the landmark Clean Air Act (CAA) of 1970, which required the EPA to grant waivers to California except in certain limited circumstances, among other provisions. 1970 was also the year in which the Environmental Protection Agency (EPA) was established, inheriting and consolidating the environmental responsibilities of the federal government. In 1990, the Clean Air Act was amended to allow other US states to adopt California’s standards.

Over the following decades, California’s ability to set its own standards has been a significant force in the effort to combat climate change. To date, the EPA has approved 100+ waiver requests from the California Air Resources Board for new and amended California emissions standards. 17 other US states and the District of Columbia – representing 40% of new light-duty vehicle registrations and 25% of new heavy-duty registrations – have adopted at least some of California’s standards.

The recent joint resolutions rely upon the Congressional Review Act (CRA) of 1996, which allows Congress to nullify federal agency rules with a majority vote on a joint resolution of disapproval and a presidential signature. The 3 House and Senate joint resolutions are Advanced Clean Trucks (H.J.Res.87 passed 231-191, S.J.Res.46 passed 51-45), Heavy-Duty Omnibus Low NOx (H.J.Res.89 passed 225-196, S.J.Res.47 passed 49-46), and Advanced Clean Cars II (H.J.Res.88 passed 246-164, S.J.Res.45 passed 51-44).

The resolutions nullified, respectively, California’s requirement that manufacturers increase their percentages of near-zero and zero-emission medium- and heavy-duty vehicles (Advanced Clean Trucks); its stricter emissions standards for heavy-duty vehicles (Heavy-Duty Omnibus Low NOx); and its phaseout of the sale of gas-powered vehicles by 2035 (Advanced Clean Cars II). 10 other states had adopted Advanced Clean Trucks, 9 states had adopted Heavy-Duty Omnibus Low NOx, and 11 states and Washington DC had adopted Advanced Clean Cars II.

Only 20 joint resolutions of disapproval have been passed by Congress under the CRA, despite 400+ resolutions being introduced. In large part, this is because they generally need support from both chambers and the president (unless Congress can override a veto with a 2/3 majority). Also, Congress has only 60 days of continuous session from the date a rule is submitted to Congress to introduce a resolution. In practice, when a rule has not been submitted to Congress, the 60-day period can be initiated when the Government Accountability Office (GAO) issues an opinion – typically in response to a request – that the rule is subject to Congressional review.

Because of the above, joint resolutions of disapproval usually only become a meaningful factor after a major transition of power like a midterm or presidential election, in some cases overturning “midnight” rules from the outgoing administration. The executive branch can withdraw rules on its own but new rulemaking can take longer than a joint resolution and be subject to reversal under a new administration. (Agencies are barred from reissuing rules that were disapproved by Congress.)

California Governor Gavin Newsom plans to fight the expected loss of California’s waivers. The key legal question appears to be whether a waiver is a rule with “general applicability” or an action with “particular applicability” (i.e. to California). The nonpartisan GAO, which issues formal opinions on whether agency actions are considered rules under the CRA, has opined that EPA waivers are not rules subject to review under the CRA but rather case-specific adjudications. The nonpartisan Senate parliamentarian has concurred with the GAO (or deferred to the GAO, according to Republicans), although neither opinion is binding.

Notably, California’s EPA waivers were not previously submitted to Congress for review and were only submitted by Trump’s EPA in late Feb 2025, triggering the 60-day period. Democrats are decrying Republicans’ use of this tactic, saying this could mean that decades-old policies (e.g. state Medicaid waivers) that were not previously submitted to Congress could be reviewed under the CRA and rescinded.

Republicans are saying that agencies carry the primary responsibility for determining whether agency actions meet the definition for a rule – i.e. the Trump EPA’s submissions to Congress mean that the waivers are rules. Confusingly, the EPA’s submissions to Congress seem to explicitly state that the waivers are not rules and that the CRA does not apply. This contradiction may have been intended to throw the question into Congress’ lap without incurring any institutional risk stemming from a departure from established precedent. (When an agency departs from established precedent, it generally must acknowledge and provide clear reasoning for its changed position.)

Much depends on how California’s expected lawsuit pans out. If the courts determine that California’s waivers have general applicability, its other waivers (past and future) could be on the chopping block – not to mention a potential array of other agency actions that could be determined in retrospect to have general applicability. The lawsuit’s progress through the courts may be limited by the CRA’s provision that “[n]o determination, finding, action, or omission under this chapter shall be subject to judicial review” – the scope of this, however, is somewhat unclear.

While the end of California’s emissions waivers is popular amongst many automakers and the gasoline industry, it will be a blow to the embattled US electric vehicle (EV) industry. US EV sales dropped 5% in Apr 2025, even while the broader vehicle market grew by 10%. Tesla sales in the US fell even more, by 13%. Trump’s tariffs and the Republican tax bill’s ending of EV incentives and its new registration fees for EV owners will only drag sales down further. While these dynamics are unlikely to reverse the tide in favor of conventional vehicles, it will, at a minimum, slow the adoption of EVs and the related capital investments in infrastructure and R&D.

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