How much weight a court gives an agency’s reading of a statute has been substantially revised, with significant consequences for regulated parties.
The prior framework directed courts to defer to a reasonable agency interpretation where the statute was ambiguous. That framework was overruled, and courts now exercise independent judgment in determining the best reading of a statute.
What remains. An agency’s interpretation may be persuasive in proportion to its thoroughness, consistency, and the agency’s expertise — a respect-based approach rather than binding deference. Where Congress has expressly delegated authority to an agency to define a term or fill a gap, courts respect the delegation and review for whether the agency acted within its bounds.
Deference to agency interpretation of its own regulations survives in narrowed form, requiring genuine ambiguity, a reasonable reading, and that the interpretation be the agency’s authoritative position implicating its substantive expertise and reflecting fair and considered judgment.
The major questions principle requires clear congressional authorisation for agency action of vast economic and political significance.
Arbitrary and capricious review of agency action is unaffected and remains the most common route to setting aside a rule — requiring reasoned decisionmaking, consideration of important aspects of the problem, and a response to significant comments.
Practical effect. Challenges to agency interpretation are more viable, and regulated parties should reassess positions taken in reliance on prior guidance.