The Supreme Court\u27s decision in Chevron U.S.A. Inc. v. Natural Resources Defense Counsel, Inc. dramatically expanded the circumstances in which courts must defer to agency interpretations of statutes. The idea that deference on questions of law is sometimes required was not new. Prior to Chevron, however, courts were said to have such a duty only when Congress expressly delegates authority to an agency to define a statutory term or prescribe a method of executing a statutory provision. Outside this narrow context, whether courts would defer to an agency\u27s legal interpretation depended upon multiple factors that courts evaluated in light of the circumstances of each case. In other words, deference was not mandatory, but was grounded in the exercise of judicial discretion.
Chevron expanded the sphere of mandatory deference through one simple shift in doctrine: It posited that courts have a duty to defer to reasonable agency interpretations not only when Congress expressly delegates interpretative authority to an agency, but also when Congress is silent or leaves ambiguity in a statute that an agency is charged with administering. The Court in Chevron blandly referred to such gaps and ambiguities as implied delegations of interpretative authority and treated these implied delegations as equivalent to express delegations. Chevron\u27s equation of gaps and ambiguities with express delegations turned the doctrine of mandatory deference, formerly an isolated pocket of administrative law doctrine, into a ubiquitous formula governing court-agency relations. With this one small doctrinal shift, the Court effected a fundamental transformation in the relationship between courts and agencies under administrative law
