On September 14, 2026, EPA Administrator Lee Zeldin signed a final rule partially repealing the Biden-era “Carbon Pollution Standards” governing greenhouse gas (GHG) emissions from fossil fuel-fired electric generating units (EGUs). The rule, formally titled Partial Repeal of the Carbon Pollution Standards for Fossil Fuel-Fired Electric Generating Units, published in the Federal Register on September 17, 2026, and takes effect November 16, 2026 (Docket ID No. EPA-HQ-OAR-2025-0124; FRL-12674-02-OAR).
Notably, this rule change is a “partial” repeal. EPA is rescinding the emission guidelines that applied to existing coal-fired steam units, but is leaving the Phase 1, efficiency-based New Source Performance Standards (NSPS) for new and modified units in place for now, while it works through a broader proposal that would eliminate those too.
Regulatory History
The current rule is the latest turn in a decade-plus of back-and-forth over how, or whether, EPA regulates GHGs from power plants under Clean Air Act Section 111:
- 2015 – EPA finalized the Clean Power Plan, the first attempt to regulate GHGs from existing power plants, built around a “generation-shifting” approach to reducing emissions across the grid. While the rule officially took effect in 2015, there were several petitions filed resulting in revisions.
- 2019 – EPA repealed the Clean Power Plan and replaced it with the narrower Affordable Clean Energy (ACE) Rule, which limited “best system of emission reduction” to heat-rate improvements at individual coal units.
- 2021 – The D.C. Circuit vacated the ACE Rule, reviving uncertainty over EPA’s authority and approach.
- 2022 – The Supreme Court’s decision in West Virginia v. EPA held that EPA could not use a generation-shifting approach without clear congressional authorization, invoking the major questions doctrine and reshaping the boundaries of future rulemakings.
- April 2024 – EPA finalized the 2024 Carbon Pollution Standards, its response to West Virginia. The rule set NSPS for new, modified, and reconstructed sources under Section 111(b) (40 CFR Part 60, Subparts TTTT and TTTTa) and separate emission guidelines for existing coal-fired steam units under Section 111(d) (Subpart UUUUb). The existing-source guidelines required long-term coal units to install 90% carbon capture and storage (CCS) by 2032, while new baseload combustion turbines faced a similar CCS or hydrogen co-firing requirement (Phase 2) on top of efficiency-based standards that applied more broadly (Phase 1).
- June 2025 – The current EPA proposed repealing the 2024 standards, questioning the technical and legal basis for the rule following the change in administration.
- September 2026 – EPA finalized the partial repeal described above and simultaneously issued a supplemental proposal to rescind what remains.
What the Final Rule Does
The September 2026 final rule:
- Eliminates the Subpart UUUUb emission guidelines entirely, ending GHG compliance obligations for existing coal-fired steam EGUs and relieving states of the requirement to submit Section 111(d) state plans for those units.
- Repeals the Phase 2, CCS-based standards that would have applied to coal units undergoing large modifications and to new baseload combustion turbines, along with the associated 40% natural gas co-firing requirement for medium-term coal units.
- Leaves in place the Phase 1, efficiency-based NSPS under Subparts TTTT and TTTTa for new, modified, and reconstructed EGUs, though EPA’s preamble acknowledges “meritorious concerns” about their achievability and signals these, too, are under review. Stationary combustion turbines subject to these subparts and operated as base load units may need to implement combined cycle technology in order to meet the output-based emission limits.
EPA grounded the repeal in its own reassessment of the “best system of emission reduction” analysis, concluding that 90% CCS and high-percentage natural gas or hydrogen co-firing were not adequately demonstrated, were not cost-reasonable, and could not be achieved within the compliance timelines set in 2024.
What Happens Next
EPA’s supplemental proposal, issued the same day, would go considerably further: it seeks to rescind all remaining GHG standards for fossil fuel-fired EGUs, arguing that EPA “lacks authority to regulate GHG emissions from EGUs under Section 111 of the Clean Air Act.” The agency’s legal theory leans on the argument that GHGs are a globally, rather than locally or regionally, distributed pollutant, and separately invokes the major questions doctrine from West Virginia. A virtual public hearing on the supplemental proposal is scheduled for October 1, 2026, with public comments due November 2, 2026. Nothing in the supplemental proposal is final, and the Phase 1 standards remain legally enforceable unless and until that rulemaking is completed.
The partial repeal is also already being challenged in court. On September 17, 2026, the Natural Resources Defense Council, American Lung Association, American Public Health Association, Clean Air Council, Clean Wisconsin, and Environmental Defense Fund filed suit in the U.S. Court of Appeals for the D.C. Circuit, arguing that repealing GHG standards without a replacement abdicates EPA’s statutory obligation to regulate the power sector’s largest source of carbon emissions. Litigation of this kind typically takes months to years to resolve, but it adds another layer of uncertainty to long-term compliance and investment planning.
Industry Impact
For owners and operators of existing coal-fired steam EGUs, the immediate effect is significant compliance relief: the CCS and co-firing deadlines under Subpart UUUUb, along with associated state-plan obligations, are off the table, at least for now. For new and modified gas-fired and coal-fired units, Phase 1 efficiency-based NSPS obligations remain in effect, but the Phase 2 CCS-based requirements that would have applied to high-capacity-factor (“baseload”) combustion turbines are gone. That distinction matters most for the wave of new natural gas capacity now being planned to meet surging demand from data centers and other large loads.
For compliance planning purposes, entities with existing coal steam units should treat their Subpart UUUUb obligations as rescinded as of the November 16, 2026 effective date, while entities developing new or modified fossil EGUs should continue planning around NSPS requirements under Subparts TTTT and TTTTa, while watching the supplemental rulemaking and the pending D.C. Circuit litigation closely, since either could still change that picture before new projects reach commercial operation.
If you have any questions about this regulatory update, please reach out to your local Trinity office or call our main line at 866.409.8476.
