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On July 29, 2025, USEPA Administrator Lee Zeldin announced the agency’s reconsideration and proposed repeal of all greenhouse gas (GHG) emissions standards for light, medium, and heavy-duty vehicles and engines (extending to the Biden administration electric vehicle mandate as well). EPA further proposes repeal of the 2009 Endangerment Finding, which established the legal foundation for regulating vehicle GHG emissions under section 202 of the Clean Air Act. EPA’s proposed rescission of the Endangerment Finding would have the ancillary effect of withdrawing the legal foundation for EPA’s regulation of GHG emissions from stationary sources under the Clean Air Act.

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The 2009 Endangerment Finding was interpreted broadly over the last 16 years impacting state implementation plans, the new source review program, and the regulation of GHG emissions from various fossil fuel related industrial and utility sectors. In short, the Endangerment Finding had a significant impact beyond just mobile sources.

EPA cites practical and legal reasons for seeking to repeal the Endangerment Finding. On the practical side, EPA concludes that removing GHG emission regulations will reduce the cost of cars and consumer products more generally. Regarding the legal rationale for repeal, EPA references recent decisions from the Supreme Court of the United States further limiting the scope of agency authority. More specifically, EPA justifies its proposal on several alternative legal interpretations:

EPA references intervening Supreme Court rulings, particularly West Virginia v. EPA (2022), which expanded the major questions doctrine, to argue that it now lacks clear congressional authorization to regulate GHG emissions under the Clean Air Act. The 2007 SCOTUS decision in Massachusetts v. EPA (finding that GHGs are pollutants regulated under the Clean Air Act) did not address the major questions doctrine which EPA asserts must be considered now.

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EPA concludes that the "text, structure, and history" of the Clean Air Act indicates that Section 202 was intended to address local and regional air pollution, not global phenomena like climate change. EPA reasons that a pollutant must be found to endanger public health and welfare "by its presence in the ambient air” as a predicate for regulation under the Act. Greenhouse gases impact public health and welfare only indirectly, through global effects, rather than local or regional exposure.

The Obama Administration era EPA improperly separated the issuance of its 2009 Endangerment Finding from the subsequent regulatory rulemaking applying that finding, thereby bypassing the cost considerations and scientific scrutiny that would have normally been undertaken during the rulemaking process.

New motor vehicles do not meaningfully contribute to climate change since they constitute a small fraction of global GHG emissions.

The 2009 Endangerment Finding was ostensibly limited to the evaluation of motor vehicle emissions, yet it also covered gases not emitted by vehicles, such as perfluorocarbons and sulfur hexafluoride.

The threshold for when pollution "endangers" public health or welfare cannot be met by "any predicted negative impact" as concluded in the 2009 Endangerment Finding. That standard provides no effective limit on the EPA's regulatory powers.

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If the Endangerment Finding is rescinded, it will likely have broad implications for regulated sources emitting GHGs. Because the Endangerment Finding established a clear basis for federal preemption of state common law lawsuits (e.g., nuisance) against those sources, repeal of the Endangerment Finding may once again permit such litigation.

Mobile source tailpipe emissions are the largest source of ozone precursor emissions impacting the southeastern Wisconsin nonattainment regions. Eliminating GHG limits on mobile source emissions will remove an important regulatory tool for reducing tailpipe emissions in upwind areas that impact southeastern Wisconsin, such as Chicago and Gary. This could exacerbate ozone levels in the upper Midwest.

The proposal will be open for public comment through September 2, 2025 – Docket EPA-HQ-OAR-2025-0194. We continue to monitor these developments. If you have questions about how this proposed rule may affect your business, please contact your Michael Best attorney or a member of our team listed on this alert.

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