The U.S. Supreme Court has blocked six U.S. states from suing major power companies to force cuts in greenhouse gas emissions that the states blame for climate change.

In an unanimous decision Monday, the court ruled that only the U.S. government's Environmental Protection Agency has the authority to regulate greenhouse gas emissions. The eight justices overturned a lower court decision that would have allowed the six states and environmental groups to proceed with the lawsuit and bring the five power companies to trial.

The Supreme Court ruling is a victory for the power companies and the Obama administration, which sided with them in the case. It also represents the court's most important opinion on climate change since its 2007 decision that confirmed the EPA's authority to regulate emissions.

Justice Ruth Bader Ginsburg, writing for the court, said the U.S. Clean Air Act passed by Congress leaves “no room” for what she called a “parallel track” of enabling federal judges to control emissions. She also said that if the plaintiffs are not satisfied with the EPA's eventual decision on emission regulations, they can have their case reviewed in court.

A lawyer who represented the conservation groups called on the EPA to impose new emission regulations “without delay.”

The six states who filed the lawsuit are California, Connecticut, Iowa, New York, Rhode Island and Vermont. They complained that the power companies were creating a public nuisance by contributing to climate change.

The five power companies involved in the case are American Electric Power Co. of Ohio, Duke Energy Corp. of North Carolina, Southern Co. of Georgia, Xcel Energy Inc. of Minnesota, and the government-owned Tennessee Valley Authority.