The 6th Circuit Court of Appeals ruled that the Clean Air Act's citizen suit provision cannot be used to compel state regulators to enforce a CAA requirement to limit pollution from new and modified sources. The court held that plaintiffs lacked standing to bring suit against Ohio EPA, and rather should have brought the action against U.S. EPA in its oversight role.

The Sierra Club and three Ohio residents argued that they could sue Ohio EPA to require it to make best available technology ("BAT") determinations before issuing permits to small emitters. A 2006 state law exempted sources that emit less than 10 tons of air pollution a year from the BAT requirement in an effort to lessen the burden of air pollution compliance for small businesses and facilitate issuance of permits to install and operate by Ohio EPA.

The court said the plaintiffs could sue the U.S. EPA for its failure to impose an administrative penalty on Ohio or for failing to administer the BAT requirement itself. “If they want to sue a regulatory agency, they can do so. They have simply chosen the wrong one," the court said.