Dive Brief:

• The U.S. Supreme Court has rejected a second appeal by a group of states who say they face irreparable harm if the Environmental Protection Agency is allowed to continue enforcing new emissions rules that went into effect last year, Reuters reports. 
• The Justices previously ruled that regulators should have done a cost-benefit calculation before beginning to write the regulations and sent the case back to the D.C. Circuit Court, which then ruled EPA could continue enforcing the Mercury and Air Toxics Standards (MATS) while the agency reworked the rule.
• The rules went into effect in 2015, and were updated earlier this year. Bloomberg reports generators fear they could cost customers almost $10 billion annually, while federal officials believe MATS will prevent up to 11,000 premature deaths each year.

Dive Insight:

The court battle over the Obama administration's MATS rule will continue, even as a group of 20 states faced a new setback from the Supreme Court.

Bloomberg reports that Murray Energy has filed a lawsuit challenging the EPA's decision earlier this year, that the benefits of the rule outweigh the costs. The high court's decision this week addressed whether the Circuit Court erred in allowing the rules to stay in place as they were being reworked,

“MATS offers tremendous benefits for the American people by protecting their health, at reasonable costs to industry," Sanjay Narayan, a managing attorney for the Sierra Club, said in a statement. “The Supreme Court correctly rejected the latest industry challenge to these vital protections against dangerous, toxic pollutants—pollutants which have, until these Standards, put the health of young children across the country at risk.”

Sierra Club said that EPA's new cost assessment of the rule was found to be "relatively modest, especially in relation to the massive health benefits of the protections." Last year, the group estimated more than 20 GW of coal-fired generation would come offline before the end of the year, largely due to the MATS rule.

The Supreme Court's 2015 decision to strike down the MATS rule was written by the late Justice Scalia, who said that the EPA should have factored in costs at the beginning. But the ruling did not question the agency's ability to regulate mercury and other air toxins, sending it back to the D.C. Circuit.

In ruling that the EPA must consider compliance costs when making new rules, it could shift the way EPA interacts with energy stakeholders and state lawmakers in ways that remain to be seen. And as the agency addressed that issue, the D.C. Circuit determined regulators could continue enforcing the rules while the fix was being completed.