The Environmental Protection Agency must consider costs when it regulates power plants under the Clean Air Act. Decided June 29, 2015 (argued March 25, 2015). Opinion of the Court: Antonin Scalia → go there Dissenting: Kagan. Topic: Administrative law. Michigan v. Environmental Protection Agency, 576 U.S. 743 (2015), is a landmark United States Supreme Court case in which the Court analyzed whether the Environmental Protection Agency must consider costs when deciding to regulate, rather than later in the process of issuing the regulation. Wiki link