In this case, environmental activist groups petitioned the EPA seeking to require the EPA to add coal mines to the EPA's list of regulated stationary sources of air pollution. The EPA declined and the plaintiffs sued. The court upheld EPA's denial of the plaintiffs' petition on the basis that EPA was within its authority to add coal mines to the regulated list so as to focus on more "significant" sources of air pollution before it turned its attention to coal mines. WildEarth Guardians v. United States Environmental Protection Agency, et al., No. 13-1212, 2014 U.S. App. LEXIS 8878 (D.C. Cir. May 13, 2014).