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

Industry groups and some 20 states had challenged the E.P.A.’s decision to regulate the emissions, saying the agency had failed to take into account the punishing costs its rule would impose.

The Clean Air Act required the regulation 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.

Writing for the majority, Justice Antonin Scalia wrote: “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. Statutory context supports this reading.”

The E.P.A. had argued that it was not required to take costs into account when it made the initial determination to regulate. But the agency added that it had done 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, does not strike down the rule, but it means the E.P.A. will have to review and rewrite it, taking costs into consideration. Industries will be expected to comply with the current rule until a revised one is issued.

“The E.P.A. will have to do more homework on costs,” said Sean Donahue, who represents environmental and public health groups that signed on to the agency’s case. “But I’m very confident that the final rule will be up and running and finally approved without a great deal of trouble. This is a disappointment. It’s a bump in the road, but I don’t think by any means it’s the end of this program.”

http://www.nytimes.com/2015/06/30/us/supreme-court-blocks-obamas-limits-...