The 1970 amendments to the Clean Air Act required states to meet federally mandated air quality standards within a statutorily specified period of time. States were directed to submit to the Administrator of the EPA a plan to "implement, attain and maintain" the federally adopted standards within nine months of the promulgation of such standards. The EPA Administrator was required to approve implementation plans meeting the statutory criteria and to promulgate substitutes for those found deficient. A number of states included variance procedures in their implementation plans, which the EPA approved. The NRDC challenged the EPA's approval of Georgia's implementation plan on the grounds that the postponement provision of the Clean Air Act was the only method to modify the state implementation plans. The Fifth Circuit Court of Appeals held that the Georgia plan should not have been approved, and the Supreme Court granted certiorari.
