In American Trucking Ass'n v. U.S. Environmental Protection Agency (ATA I), a panel of the U.S. Court of Appeals for the District of Columbia (D.C.) Circuit shocked the administrative and environmental law worlds. There, the court, in a 2-1 decision, remanded to the U.S. Environmental Protection Agency (EPA) for reconsideration of its new air quality standards under the Clean Air Act (CAA) for ozone and particulate matter. Subsequently, the court, sitting en banc, modified ATA I, but narrowly refused to grant rehearing (ATA II).

ATA I's primary rationale, articulated by Judge Stephen Williams, was that the Agency lacked an "intelligible principle" for setting air quality standards. This holding, to some commentators, presaged the revival of the delegation doctrine, which had last been used in the 1930s to invalidate congressional grants of power to administrative agencies. These commentators foresaw a drastic reduction in the U.S. Congress' power to use broad delegations to administrative agencies as a way to regulate private industry.

There was another important, although less noted, aspect of ATA I: the court apparently ruled that the CAA did not give EPA authority to require the states to take steps to implement the new air quality standard. Hence, barring an act of Congress, the revision of the standard would do little to clean the air.