Before Mead, it was clear that the Chevron Doctrine applied to interpretations adopted in legislative rules and certain formal adjudications, but lower courts differed regarding whether it also applied to interpretative rules, policy statements, informal adjudications, advisory letters, amicus briefs.
In Mead, it was questioned whether the court should defer to the U.S. Customs Services interpretation of the Customs Act, as manifested through the many classification decisions its regional offices made annually.