The Obama administration suffered a major blow when the U.S. Supreme Court overturned federal environmental regulations that required power plants to limit emissions of mercury and other pollutants.

In a 5-4 ruling on Monday, the justices ruled that the Environmental Protection Agency (EPA) did not properly consider the costs of the regulation when it issued the landmark Clean Air Act in 2012 to control air pollution, reports The Hill. According to the High Court, the EPA should have taken into account how much it would cost utilities and the power sector industry before deciding how to set limits for the toxic air pollutants it regulated in 2011.

During the case, the EPA estimated its regulations would cost $9.6 billion per year. In turn, the EPA rules would have required coal or oil-burning plants to drastically reduce their mercury emissions, which are considered to be especially harmful to children and pregnant women.

The plaintiffs, on the other hand, argued that the new standards came with "huge costs."

The court found the $9.6 billion coast outweighed the "quantifiable benefits" from the resulting reduction in emissions.

In the majority ruling, Justice Antonin Scalia concluded that the EPA's Clean Air Act was "interpreted unreasonably when it deemed cost irrelevant to the decision to regulate power plants."

"It is not rational, never mind 'appropriate,' to impose billions of dollars in economic costs in return for a few dollars in health or environmental benefits," Scalia wrote.

Justice Elena Kagan wrote a dissenting opinion stating that the regulations would have kept people healthier and therefore saved a lot of money. The "EPA conducted a formal cost-benefit study which found that the quantifiable benefits of its regulation would exceed the costs up to nine times over -- by as much as $80 billion each year," she wrote.

"Those benefits include as many as 11,000 fewer premature deaths annually, along with a far greater number of avoided illnesses," Kagan added.

Republicans, such as Sen. Steve Daines of Montana, applauded the Supreme Court decision. "#SCOTUS took an important step to help ensure the EPA takes into account the true cost of excessive regulations on the American people," he wrote on Twitter.