On April 29, the Supreme Court upheld the authority of the U.S. Environmental Protection Agency (EPA) to regulate cross-state air pollution rules (CSAPR), also known as the Clean Air Act’s “good neighbor” provision or the “Transport Rule.” The law will require many older coal-fired power plants to either install new technologies or shut-down, in an effort to prevent air pollution from crossing into neighboring states. Power utilities and 15 states had filed suit against the law. The 6-2 decision in the case, EPA v. EME Homer City Generation, L.P., reversed the 2012 decision to vacate CSAPR by the United States Court of Appeals for the District of Columbia, which had stated that the regulations were too costly and arbitrary.

The Supreme Court majority opinion found that “EPA’s cost-effective allocation of emission reductions among up-wind States is a permissible, workable, and equitable interpretation of the Good Neighbor Provision.” Justice Ginsburg wrote the opinion of the Court and was joined by Chief Justice Roberts and Justices Kennedy, Breyer, Sotomayor and Kagan. The dissent was written by Justice Scalia, who was joined by Justice Thomas. Justice Alito recused himself from the case.

Under CSAPR, 28 Midwestern and Appalachian states will be required to cut power plant emissions of ozone-forming compounds including sulfur dioxide, nitrogen oxide, and particulate matter that become airborne and travel downwind into neighboring states. According to the EPA, exposure to ozone and particulate matter is accountable for one in 20 U.S. deaths, 200,000 nonfatal heart attacks, 90,000 hospital admissions and contributes to 2.5 million cases of childhood asthma. EPA estimates that CSAPR would save $280 billion annually in healthcare costs and avoid 34,000 premature deaths a year.

The Supreme Court heard oral arguments for the case in December 2013. The Supreme Court heard oral arguments for a separate case in February 2014 regarding whether EPA’s authority to regulate the greenhouse gas emissions of new motor vehicles also extends to stationary sources, such as existing power plants. A decision in that case, Utility Air Regulatory Group v. Environmental Protection Agency, is expected this summer.