The U.S. Supreme Court has elected to hear a legal dispute over the scope of the authority granted to the Environmental Protection Agency (EPA) under the Clean Air Act to regulate greenhouse gas (GHG) emissions from existing power plants. In orders issued October 29, the Court granted certiorari to four petitioners — West Virginia, North Dakota, the North American Coal Corporation, and Westmoreland Mining Holdings LLC — seeking reversal of a September 2020 D.C. Circuit Court of Appeals decision striking down the Affordable Clean Energy (ACE) rule.

The ACE rule was promulgated under Section 111(d) of the Clean Air Act, which grants EPA the authority to regulate existing sources of air emissions if EPA has already promulgated a standard for that industry under Section 111(b) of the statute. The ACE rule established GHG emission standards that could be achieved at an individual facility level. It also included the repeal of EPA’s predecessor 111(d) rule, the Clean Power Plan, which would have required the industry to shift electricity generation to cleaner resources in order to comply.

The question presented to the Supreme Court in each of the petitions for certiorari in the ACE rule case varied somewhat, but can be boiled down to this: Does Section 111(d) of the Clean Air Act allow EPA to pass a rule so far reaching that it would regulate the way an entire industry operates, or is EPA’s authority under that section limited to standards that can be achieved by individual sources? Essentially, the petitioners are asking the Supreme Court to weigh in on what model EPA may use under Section 111(d) to reduce GHGs from existing power plants — the ACE rule, the Clean Power Plan, or something in between.

The petitioners are hopeful the Court will issue a decision in the ACE case limiting EPA’s reach under 111(d). Their hope is not far-fetched, given that the Court already weighed in on the Clean Power Plan in 2016, issuing an unprecedented stay of the rule while the case made its way through the courts. However, the breadth of the eventual decision may be somewhat limited, as the Court has only been asked to weigh in on the scope of Section 111(d). The Court also declined to hear an additional question posed by one petitioner regarding whether power plant regulations already adopted under Section 112 of the Clean Air Act preclude EPA from regulating the industry under Section 111(d). A decision is expected in summer 2022.