On Feb. 4, the U.S. Department of Justice, on behalf of EPA, filed suit against Westar Energy, Inc. in St. Marys, Kansas for allegedly failing to install the best available control technology at one or more of its coal-fired power plants. The complaint, brought under the New Source Review ("NSR") provisions of the Clean Air Act, revives a line of NSR enforcement cases many thought was dead during the previous administration -- and revives an initiative targeting coal-fired power plants that the Clinton administration began in 1999. While there remains little clear guidance as to what projects at existing facilities may trigger NSR, the complaint against Westar Energy, Inc. is a signal to utilities to prepare for renewed regulatory attention to NSR enforcement and potential litigation over past, and potentially future, modifications.