Via The New York Times:

WASHINGTON — The Supreme Courton Monday blocked one of the Obama administration’s most ambitious environmental initiatives, one meant to limit emissions of mercury and other toxic pollutants from coal-fired power plants.

Justice Antonin Scalia wrote the majority opinion in the 5-to-4 decision, joined by the court’s more conservative members.

Industry groups and some 20 states challenged the Environmental Protection Agency’s decision to regulate the emissions, saying the agency had failed to take into account the punishing costs its regulations would impose.

The Clean Air Act required the regulations to be “appropriate and necessary.” The challengers said the agency had run afoul of that law by deciding to regulate the emissions without first undertaking a cost-benefit analysis.

The agency responded that it was not required to take costs into account when it made the initial determination to regulate. But the agency added that it did so later in setting emissions standards and that, in any event, the benefits far outweighed the costs.

The two sides had very different understandings of the costs and benefits involved. Industry groups said the government had imposed annual costs of $9.6 billion to achieve about $6 million in benefits. The agency said the costs yielded tens of billions of dollars in benefits.

The decision, Michigan v. Environmental Protection Agency, No. 14-46 was a setback for environmentalists.