The U.S. Supreme Court denied a request Thursday to block the EPA’s mercury-emissions rule while legal challenges proceed, handing a temporary victory to the the Obama administration and environmental groups.

Twenty states asked lower courts to block the rule’s enforcement while their case against the EPA is ongoing. The D.C. Circuit Court of Appeals denied their motion in December, and the states turned to Chief Justice John Roberts, who oversees stay requests from the D.C. Circuit. Although Roberts can refer those requests to the entire Supreme Court for consideration, he rejected it on his own authority as the circuit justice.

The EPA adopted its long-awaited emissions rule in February 2012, targeting mercury and other toxic byproducts of fossil fuels emitted by power plants. Agency officials estimated the new regulations would reduce those emissions by 90 percent and prevent about 11,000 premature deaths each year.

Under the Clean Air Act, the EPA has broad authority to regulate residual emissions from power plants and other major sources of air pollution when the agency considers it “appropriate and necessary.” Almost two-dozen states challenged the rule in court, arguing the EPA failed to consider the financial burden of its regulations when it decided to intervene. The EPA countered that while it did not weigh that burden at the beginning of its process, the agency did consider it multiple times thereafter.