Supreme Court declines mercury rule challenge: UpdateOREANDA-NEWS. June 14, 2016. The US Supreme Court will not review renewed challenges from states to the Environmental Protection Agency's (EPA) mercury and air toxics rule.

The court today denied an appeal filed by a group of 20 states asking for a review of whether the DC Circuit Court of Appeals acted correctly last year in leaving the mercury rule in place after the Supreme Court said EPA failed to consider costs before issuing the regulations.

The states, led by Michigan, had said EPA lacked the authority to enforce the rule because of the high court's June 2015 decision. But EPA argued that it viewed the case as moot because the agency issued a new finding on the cost of regulating mercury in April.

The office of Michigan attorney general Bill Schuette (R) said it was "very disappointed" in the decision.

"The US Supreme Court correctly awarded Michigan a victory last year in this case of unconstitutional federal overreach. The EPA blatantly refused to follow that ruling," Schuette spokeswoman Andrea Bitely said.

EPA said it was pleased the court allowed the rule to remain in place. "These practical and achievable standards cut harmful pollution from power plants, saving thousands of lives each year and preventing heart and asthma attacks," the agency said.

The mercury rule required a 90pc reduction in emissions from coal- and oil-fired power plants by April 2015, although about 180 units had sought and received one-year extensions as of last fall.

No industry groups or companies joined the 20 states in the latest Supreme Court appeal. A separate group of seven states, led by Colorado, supported the appeal, while another 15 sided with EPA.

The Supreme Court last June ruled that EPA failed to consider costs before it decided it was "appropriate and necessary" to regulate power-sector mercury emissions. The 5-4 decision, authored by the late Antonin Scalia, did not address the standards themselves.

The justices sent the case back to the DC Circuit, which had previously upheld the regulations and, in December, rejected a request from states and industry to vacate the rule. The Supreme Court rejected similar requests in February.

In response to the court's decision, EPA in April issued a finding that the costs still justified regulating mercury emissions from power plants. Coal producer Murray Energy on 25 April filed a lawsuit challenging EPA.