The Environmental Protection Agency required several States to revise plans addressing interstate ozone pollution under the Clean Air Act’s Good Neighbor Provision. The agency disapproved portions of those plans and issued federal plans while the States sought review. The Supreme Court of the United States considered whether the federal implementation plans should be stayed while the litigation continued. The Court granted the applications for a stay, concluding that the States had made the required showing under the governing standard and that the lower courts’ review would likely take substantial time. The decision addressed the interim effect of the agency’s pollution controls rather than finally resolving the merits of the statutory challenges. Separate opinions disagreed about the statutory framework, the applicants’ likelihood of success, and the practical consequences for air-quality regulation.