Generally, to be accorded Chevron deference, the agency’s interpretation of an ambiguous statute must be permissible, which the court has defined to mean “rational” or “reasonable.” In determining the reasonableness of a particular construction of a statute by the agency, the age of that administrative interpretation as well as the congressional action or inaction in response to that interpretation at issue can be a useful guide, if the Congress was aware of the interpretation when it acted or refrained from action, and when the agency’s interpretation is not inconsistent with the clear statutory language.
In subsequent cases, the Supreme Court has narrowed the scope of Chevron deference, holding that only the agency interpretations reached through formal proceedings with the force of law, such as adjudications, or notice-and-comment rulemaking, qualify for Chevron deference, while those contained in opinion letters, policy statements, agency manuals, or other formats that do not carry the force of law are not warranted a Chevron deference. In such cases, the Court may give a slightly less deferential treatment to the agency’s interpretation, giving a persuasive value under the Court’s “Skidmore deference” analysis.
Last edited by Jonathan Kim, December 2017