The DC Circuit in 2017 held that EPA overstepped its authority in the agency’s 2015 hydrofluorocarbons (HFC) regulation that required the replacement of HFCs with substitutes with lower air quality impacts. In other words, the court held that EPA has no authority to require further substitution after an entity ends its use of ozone depleting substances as required by the CAA. Mexichem Flour, Inc. v. EPA, 866 F.3d 451 (D.C. Cir. 2017). EPA released guidance explaining that as a result of the court’s decision, it will not enforce the 2015 requirements and that it intends to undertake a new rulemaking to rewrite the HFC regulations. EPA’s guidance and any eventual rulemaking are likely to be challenged by environmental groups or manufacturers of HFC substitutes, who stated in a recent court filing that they will seek Supreme Court review of the DC Circuit’s decision by June 25, thus setting the stage for legal battles to come.