The US Supreme Court this week ruled that the federal government can impose limits on power plant pollution that crosses state lines, marking a victory for the Obama administration and the Environmental Protection Agency (EPA). In a 6-2 ruling handed down Tuesday, the court upheld an EPA regulation that requires 28 states to cut emissions from coal-burning plants that pollute the air in downwind states.

The Cross-State Air Pollution Rule was met with lawsuits from power companies and more than a dozen states when it was implemented in 2011, and was blocked by a federal appeals court in 2012. The Supreme Court has now reversed that decision, ruling that the EPA has the authority, under the Clean Air Act, to impose emissions reductions in upwind states. The EPA argued that the rule would improve air quality in downwind states, preventing more than 30,000 premature deaths and other illnesses. The EPA's regulations focus on nitrogen oxide and sulfur dioxide emissions, which have been linked to cardiovascular and respiratory illnesses. The White House has made cutting emissions from coal-burning power plants a cornerstone of its environmental agenda.

Opponents say the EPA infringed on states' rights

Power companies and some upwind states contested the rule, arguing that it infringes on states' rights. Texas, Ohio, and 12 other states believed it was their responsibility to determine their respective effects on pollution levels in downwind states, and that the EPA declined to work cooperatively on the issue. They also criticized the EPA's methodology for determining the appropriate levels of reduced emissions, claiming that some states were forced to cut more than their fair share, but Justice Ruth Bader Ginsburg sided with the EPA, writing that the complexities of the situation "are not so simple."

"Most upwind states contribute to pollution to multiple downwind states in varying amounts," Ginsberg wrote on behalf of the majority opinion. Justices Antonin Scalia and Clarence Thomas argued in dissent, while Justice Samuel Alito was recused.

The EPA estimates that its rules would impose annual costs of about $800 million on power companies, compared to the $1.6 billion in annual expenditures under current rules, implemented under the George W. Bush administration in 2005. The federal agency says these costs will be balanced in the long-run by greater savings in healthcare expenses, which it estimated to be in the hundreds of billions.

Experts say the ruling could have implications for future regulations, making it more difficult to mount legal challenges to federal air quality acts. Later this year, the EPA will announce plans to reduce carbon dioxide emissions under new Clean Air Act rules.

"It’s a big win for the EPA, and not just because it has to do with this rule," said Jody Freeman, director of Harvard's environmental law program, told the New York Times. "It's the fact that it's setting the stage and creating momentum for what’s to come."