Colorado v. EPA - Regional Haze Plan Challenge

CO Attorney General Press Releases

Filed March 4th, 2026

Detected March 5th, 2026

Summary

Colorado, supported by 21 other states, has sued the EPA challenging the agency's disapproval of its regional haze plan. The EPA rejected the plan, which included coal plant retirement dates, citing concerns about uncompensated takings and insufficient assurances of implementation.

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What changed

Colorado Attorney General Phil Weiser, joined by 21 other state attorneys general, has filed a petition with the U.S. Court of Appeals for the Tenth Circuit challenging the EPA's disapproval of Colorado's regional haze State Implementation Plan (SIP). The EPA rejected the SIP, which aimed to reduce air pollution and improve air quality in natural areas, based on concerns that the inclusion of voluntary coal plant retirement dates constituted uncompensated takings and lacked necessary assurances for implementation. The state argues that these retirement decisions were voluntary agreements by utilities to comply with various laws.

This action is critical for regulated entities, particularly energy companies, as the EPA's disapproval could lead to the imposition of a federal implementation plan if the court does not overturn the decision. The outcome will impact how states can incorporate voluntary emissions reduction measures into their SIPs and could set a precedent for state authority in environmental regulation under the Clean Air Act. Companies involved in or affected by Colorado's regional haze plan should monitor the litigation closely, as it may influence future compliance strategies and regulatory approaches to air quality management.

What to do next

Monitor litigation challenging EPA's disapproval of Colorado's regional haze SIP.
Assess potential impact of EPA's decision on state implementation plans nationwide.
Review Clean Air Act regulations concerning state implementation plans and federal disapproval.

Source document (simplified)

Attorney General Phil Weiser sues EPA to defend Colorado’s plan to fight air pollution and regional haze

March 4, 2026 (DENVER) – Attorney General Phil Weiser today filed a petition with the U.S. Court of Appeals for the Tenth Circuit in Denver challenging the Trump administration’s disapproval of Colorado’s regional haze plan to reduce air pollution and improve air quality in some of the region’s most cherished natural areas.

Under the Clean Air Act and the federal Regional Haze Rule, states are required to improve air quality in national parks, like Rocky Mountain National Park, and wilderness areas. The Colorado Air Quality Control Commission adopted air quality regulations to address regional haze that account for expected closure of coal plants to comply with the Clean Air Act, help the state meet its statutory greenhouse gas reduction goals, and reduce air pollution. The coal plant retirement dates were included in Colorado’s regional haze state implementation plan, or SIP, and submitted to EPA for approval.

The EPA, however, rejected the state’s SIP in its entirety in a notice printed in the Federal Register on Jan. 26. EPA’s disapproval is largely based on its determination that Colorado fails to provide the “necessary assurances” that it could implement all the elements of the SIP, because the plan included closure dates for various coal-fired power plants, which were all voluntarily agreed to when the plan was adopted. EPA alleges that the closures might constitute uncompensated takings.

“EPA’s decision to disapprove Colorado’s regional haze state implementation plan is based on policy objections to closing coal plants and it is another example of the Trump administration intruding on state authority without any basis in law. Colorado included the closure of several coal-fired power plants in its plan based on utilities’ independent decisions to close them. Those decisions in turn were based on the utilities’ judgment that closure was the best and most cost-effective way to comply with a range of state and federal laws,” said Attorney General Weiser. “Coloradans love the outdoors, yet the EPA is threatening to weaken protections necessary to safeguard some of our most sensitive ecosystems and scenic vistas from harmful pollution.”

Because EPA fully rejected the SIP, in the absence of litigation overturning this decision, EPA is legally obligated to issue its own federal implementation plan to address regional haze in Colorado unless Colorado identifies a new plan that the agency would approve.

Read the petition for review filed with the Tenth Circuit Court of Appeals (PDF).

Media Contact:
Lawrence Pacheco
Chief Communications Officer
(720) 508-6553 office
lawrence.pacheco@coag.gov

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