States can't invoke federal law to force utilities to cut greenhouse-gas emissions, the U.S. Supreme Court ruled, shutting off one avenue for groups that advocate bolder steps against climate change.

The unanimous ruling is a victory for five companies — American Electric Power Co., Duke Energy Corp., Southern Co. and the government-owned Tennessee Valley Authority, based in Knoxville — that had been sued by six U.S. states, including California, and the city of New York.

The states, which sought a cap on emissions, argued that carbon dioxide spewed by the utilities is a public nuisance because it causes climate change. The justices said the Environmental Protection Agency was better equipped than federal judges to assess the costs and benefits of reducing greenhouse gases.