American Trucking Associations, Inc. v. Environmental Protection Agency
United States Court of Appeals for the District of Columbia Circuit
175 F.3d 1027 (D.C. Cir. 1999)
The EPA (defendant) revised national air quality standards for particulate matter and ozone without explaining the specific mechanism by which it selected the particular numeric thresholds (like moving ozone from 0.09 to 0.08), even though an internal report suggested health risk decreases at every incrementally lower level, implying no principled non-zero stopping point; industry groups (plaintiffs) challenged the rules as failing to provide standards that adequately cabin the EPA's discretion under the Clean Air Act's ambiguous delegation.
Whether, under administrative law, federal courts will automatically strike down an ambiguous statute where an agency's implementing regulations fail to articulate clear standards to guide the exercise of enforcement authority.