A coalition of environmental activists and public health advocates is urging the Supreme Court to reinstate a regulation EPA issued in 2011 to limit power plant air pollution that drifts across state lines. In August 2012, the U.S. Court of Appeals for the District of Columbia Circuit struck down the cross-state rule, which would have required 28 states to reduce emissions of nitrogen oxides and sulfur dioxide to help downwind states meet national air quality standards for ozone and fine particulate matter. The circuit court ruled that EPA exceeded its authority under the Clean Air Act by imposing federal pollution-reduction requirements without first giving states the opportunity to reduce emissions on their own terms. But the coalition argues that EPA’s interstate air rule should be restored because it was properly designed under a provision in the law that is intended to ensure that emissions from one state’s power plants do not cause harmful pollution in neighboring states. The Supreme Court, which accepted the case in June, is expected to issue a decision by June 2014.