Greenhouse gases are air pollutants, and the Environmental Protection Agency may regulate their emission under the Clean Air Act. Decided April 2, 2007 (argued November 29, 2006). Opinion of the Court: John Paul Stevens → go there Dissenting: Roberts, Scalia. Topic: Administrative law. Massachusetts v. Environmental Protection Agency, 549 U.S. 497 (2007), is a 5–4 U.S. Supreme Court case in which Massachusetts, along with eleven other states and several cities of the United States, represented by James Milkey, brought suit against the Environmental Protection Agency (EPA) represented by Gregory G. Garre to force the federal agency to regulate the emissions of carbon dioxide and other greenhouse gases (GHGs) that pollute the environment and contribute to climate change. Wiki link