The plaintiffs, a collection of environmental activist groups, sued to force the EPA to implement tougher regulatory standards for nitrogen oxide and sulfur dioxide in accordance with the Clean Air Act (CAA). The court, however, denied the plaintiff's petition on the basis that it was within EPA's discretion to take additional time to determine the new standards and study the matter further. The court noted that EPA was taking steps to update existing standards applicable to "acid rain." Center for Biological Diversity, et al. v. Environmental Protection Agency, No. 12-1238, 2014 U.S. App. LEXIS 9691 (D.C. Cir. May 27, 2014).