From the Hill, a summary of the ruling:

The Supreme Court overturned the Obama administration’s landmark air quality rule on Monday, ruling the Environmental Protection Agency (EPA) did not properly consider the costs of the regulation.

In a 5-4 ruling, the justices ruled that the EPA should have taken into account the costs to utilities and others in the power sector before even deciding whether to set limits for the toxic air pollutants it regulated in 2011.

The case, Michigan v. EPA, centers on the EPA’s first-ever limits on mercury, arsenic and acid gases emitted by coal-fired power plants, known as mercury and air toxics (MATS). Opponents, including the National Federation of Independent Business, have placed among the costliest regulations ever issued.

EPA estimated its rule, which took effect for some plants in April, would cost $9.6 billion, produce between $37 billion and $90 billion in benefits and prevent up to 11,000 premature deaths annually.

But the agency concluded that its regulatory impact analysis should have “no bearing on” the determination of whether regulations are appropriate, as set forth in the Clean Air Act.

While the rule struck down a major environmental priority of President Obama, it is not a complete loss.

The MATS rule took effect in May, and most power plant operators have already either complied by shutting plants down or retrofitting them; or have made firm plans to comply.

On a Friday appearance on HBO’s “Real Time with Bill Maher,” EPA head Gina McCarthy said she was confident the Supreme Court would rule in the EPA’s favor.

But she was not too concerned about what would happen if the ruling was against the EPA.

“This is a rule that actually regulates toxic pollution emissions from primarily coal facilities, and we think we’re going to win because we did a great job on it,” she said.

“But even if we don’t, it was three years ago, most of them are already in compliance, investments have been made, and we’ll catch up. And we’re still going to get at the toxic pollution from these facilities,” she continued.