OREANDA-NEWS. The US Supreme Court today declined to block continued implementation of federal mercury limits for coal-fired power plants.

Chief justice John Roberts rejected the request for a stay from 20 states, which had argued that keeping the Mercury and Air Toxics Standards in place would cost industry and ratepayers billions of dollars.

The quick decision by Roberts came a day after the US Environmental Protection Agency (EPA) urged the court to reject the states' request. The agency said it is "very pleased" with the decision. "These practical and achievable standards cut harmful pollution from power plants, saving thousands of lives each year and preventing heart and asthma attacks," EPA said.

Roberts, who handles stay petitions for cases in the DC Circuit Court of Appeals, denied the states' request on his own, unlike the court's decision last month to block implementation of the Clean Power Plan. In that case, Roberts consulted with his fellow justices, resulting in a 5-4 decision to grant a stay of the CO2 limits for power plants.

The states, led by Michigan attorney general Bill Schuette (R), last month asked Roberts to intervene. In addition to costing the industry billions of dollars, continued implementation of the mercury rule violates a ruling by the high court last year that said EPA did not act correctly when it issued the regulations, the states said.

Schuette's office did not immediately respond to a request for comment.

Besides Michigan, other states involved include Kansas, Ohio, West Virginia and Wyoming.

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, but did not say if the standards should remain in place while EPA addresses the cost issue.

The DC Circuit in December rejected a request from states and industry to vacate the rule. The court did not provide specific reasons for its decision but noted that EPA had said it is "on track" to respond to the Supreme Court decision by this spring.

EPA proposed a supplemental finding in November in which it said the costs of the regulation were reasonable. The agency expects to finalize the finding by 15 April 2016.

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.