In Kisor v. Wilkie, the U.S. Supreme Court significantly restricted the doctrine of Auer deference. 139 S. Ct. 2400 (2019). Under Auer (or Seminole Rock) deference, courts defer to an administrative agency’s interpretation of its own regulation when that regulation is ambiguous and the agency’s interpretation is reasonable. The split decision in Kisor leaves the doctrine intact but establishes a number of limitations to its application.
The decision is likely to impact future environmental litigation as courts will be less likely to defer to agencies’ regulatory interpretations. Agencies may respond by taking additional steps to fit their interpretations of environmental regulations within the limited scope of Auer deference recognized in Kisor.