When developing regulations governing power plants, the Environmental Protection Agency (EPA) interpreted the Clean Air Act (CAA) in a manner that deemed the cost of the regulations imposed on a power plant to be irrelevant. The D.C. Circuit had held that the EPA regulations were valid. On further review, the U.S. Supreme Court reversed. The Court held that the EPA acted unreasonably because the directive in the statute (42 U.S.C. Sec. 7412(n)(1)(A)) to determine whether the regulation was "appropriate and necessary" meant that at least some attention had to be given to cost, which included more that the expense of a power plant in complying with the regulations. The Court held that the EPA regulations were not reasonable even under the deferential standard given the agency in Chevron. Michigan, et al. v. Environmental Protection Agency, et al., No. 14-46, 2015 U.S. LEXIS 4256 (U.S. Sup. Ct. Jun. 29, 2015).