On June 11, 2025, the EPA Administrator signed a proposed rule that would repeal the greenhouse gas (GHG) emissions standards established for fossil-fired power plants under the Biden administration’s Carbon Pollution Standards (CPS) and a 2015 GHG New Source Performance Standards rule. The proposal includes two approaches: a primary proposal that would repeal all GHG standards for fossil-fired power plants based on a finding that such emissions do not “contribute significantly” to endangerment of public health and welfare, and a narrower alternative proposal that would repeal a subset of the requirements under the CPS based on a substantive, technical review of those standards. Either approach, if finalized, would significantly alter the federal regulatory landscape for GHG emissions from the power sector.

The EPA Administrator also signed a proposed rule that would repeal 2024 updates to the Mercury and Air Toxics Standards (MATS) for power plants.

Key Elements of Proposed Rule

Significant Contribution Finding. EPA's primary proposal centers on a reinterpretation of its authority under Section 111 of the Clean Air Act (CAA).

Section 111 requires EPA to list and regulate a category of major emission sources that the Administrator, “in his judgment,” finds "causes, or contributes significantly to, air pollution which may reasonably be anticipated to endanger public health or welfare" (referred to as a “Significant Contribution Finding”).

In its initial 2015 GHG standards for fossil-fired power plants, EPA asserted that it need not make a Significant Contribution Finding for emissions of GHGs for such plants because it already had made the finding for fossil-fired power plants for other pollutants. However, EPA also found that it had a “rational basis” for Section 111 regulation of GHG emissions from fossil-fired power plants on account of their high volume of such emissions.

Now, EPA is proposing to find that the agency is required, or at least is authorized to require, a pollutant-specific Significant Contribution Finding prior to regulation of that pollutant for a Section 111 source category. Further, EPA is proposing to find that GHG emissions from fossil fuel-fired power plants do not “contribute significantly” to the endangerment of the public health and welfare. This is not a direct reversal of EPA’s 2009 Endangerment Finding (which applied to mobile sources) but rather a separate, additional Section 111-specific requirement for a Significant Contribution Finding, which EPA is proposing not to find for GHGs from fossil fuel-fired power plants.

EPA also proposes to broaden the scope of what informs “significance” to take into account cost and policy factors. EPA cites the following rationales for not making the Significant Contribution Finding: the declining share of power sector GHG emissions in the U.S and globally; the absence of cost-effective controls; the attenuated causal connection between power sector GHG emissions and climate-related harms; and “because this Administration’s priority is to promote the public health or welfare through energy dominance and independence secured by using fossil fuels to generate power.”

EPA’s primary proposal would therefore rescind all GHG emissions standards for existing, new, modified, and reconstructed fossil fuel-fired electric generating units (EGUs) promulgated under CAA section 111. These standards potentially subject to repeal include the 2015 New Source Performance Standards (NSPS) (40 CFR part 60, subpart TTTT) (adopted as part of the “Clean Power Plan”) and the 2024 Carbon Pollution Standards (40 CFR part 60, subparts TTTTa and UUUUb).

Carbon Pollution Standards Repeal.As an alternative, EPA proposes a narrower repeal that would eliminate specific GHG emission standards that require the use of carbon dioxide capture and sequestration (CCS) and 40 percent co-firing of natural gas for specific subcategories of plants in the CPS because the requirements fail to meet the Section 111 requirements for a valid “performance standard.” Section 111(a)(1) provides that a performance standard must “reflect[] the degree of emission limitation achievable through the application of the best system of emission reduction which (taking into account the cost of achieving such reduction and any nonair quality health and environmental impact and energy requirements) the Administrator determines has been adequately demonstrated.”

In general, EPA finds that the system of emission reduction that forms the basis of each of the standards has not been adequately demonstrated, the costs of compliance are unreasonable, and degree of emission limitation required by the standards are not achievable due to the unlikelihood of building supporting infrastructure by the compliance deadlines. The technical findings unpinning the proposed repeal of these standards are reversals of findings EPA made in the 2023 CPS rulemaking.

The alternative proposal would leave certain performance standards unaffected including: (1) the standard that applies to new and reconstructed gas-fired combustion turbines that have a capacity factor between 20 percent and 40 percent (intermediate-load units); and (2) the phase 1 standard that applies to new and reconstructed gas-fired combustion turbines that have a capacity factor at or above 40 percent (baseload units). The proposed rule solicits comments on the viability and validity of these standards.

Economic and Compliance Impacts

EPA estimates present value compliance cost savings of approximately $19 billion (3% discount rate) or $9.6 billion (7% discount rate) over the 2026–2047 period for both the full and partial repeal scenarios. The rule would primarily impact owners and operators of fossil fuel-fired EGUs, including utilities and certain government entities. Because EPA has rescinded the “social cost of carbon” calculation, the agency’s Regulatory Impact Analysis does not assign any cost to the public from forgoing GHG reductions that would be achieved by standards subject to proposed repeal.

Mercury and Air Toxics Standards (MATS) Proposal

Simultaneous with proposing to repeal GHG standards for power plants, EPA released a proposed rule to repeal all the new regulatory requirements adopted by the 2024 Mercury and Air Toxics Standards (MATS) Rule pursuant to a mandated technology review occurring every 8 years.

In effect, the proposal would repeal the new, more stringent, filterable particulate matter (PM) standards for all coal-fired power plants and the tightened mercury standards for lignite-fired power plants. It also would repeal the requirement that all coal-fired power plants install the PM continuous emissions monitoring systems (CEMS) for demonstrating compliance with applicable MATS performance standards.

Notably, the proposal would have no effect on the initial MATS regulatory requirements that EPA adopted in 2012. Those 2012 MATS requirements would continue to apply to all affected coalfired power plants.

In support of its proposal, EPA points out that both the Biden EPA and the first Trump EPA expressly made determinations that the air toxic emissions from power plants currently do not pose “a residual risk” to human health because those risks are below the statutory standard for acceptable health risks (set at one in one million lifetime risk of cancer). As a result, the Agency has made its decision to repeal new MATS control requirements based on a technical determination that those more stringent performance standards are neither cost-effective nor based on a breakthrough of new control technologies.

Next Steps

Comments on both proposals will be accepted for 45 days following publication in the Federal Register, which is scheduled for June 17, 2025. EPA staff have informally suggested that requests for extensions of the comment deadline will likely not be granted given the tight timeframe for finalizing both proposed rules by the end of this year. EPA will conduct virtual public hearings on the two proposals 15 days after publication, with pre-registration required for speakers.