On June 23, 2014, the U.S. Supreme Court rejected the EPA’s attempt to rewrite the statutory emission thresholds for Clean Air Act regulations. The decision marked a partial victory for WLF. The case arose from a legal challenge to EPA’s controversial “tailoring rule,” which the agency adopted to allow for more expansive regulation of greenhouse gases in the wake of the Court’s earlier decision in Massachusetts v. EPA. In its brief, WLF argued that EPA had improperly seized on the Supreme Court’s narrow ruling in Massachusetts to aggrandize the agency’s authority to regulate greenhouse gas emissions. Agreeing that EPA interpreted Massachusetts too aggressively, the Court struck down the tailoring rule and held that EPA does not have the authority to rewrite applicable statutory emissions thresholds under the Clean Air Act.