The Environmental Protection Agency relied on a provision of the Clean Air Act to develop the Clean Power Plan, which addressed carbon-dioxide emissions from existing coal- and gas-fired power plants. States, power companies, and other parties challenged the agency’s authority to adopt a system that could substantially shift electricity generation across the national grid. The Supreme Court held that the agency lacked authority under the cited provision to impose that broad restructuring of the energy market. The Court applied the major-questions doctrine, requiring clear congressional authorization for an agency action of vast economic and political significance. It concluded that the statutory text did not supply that authorization and reversed the judgment below. Justice Kagan, joined by Justices Breyer and Sotomayor, dissented, arguing that the Clean Air Act authorized the agency’s approach and that the majority improperly substituted judicial policy judgments for Congress’s direction.