McCarthy added that she thinks the EPA has the legal authority to issue the rule, which the Obama administration calls the Clean Power Plan, and that, ultimately, it will be upheld in the courts.

The high court on Feb. 9 issued a 5-4 ruling that put a temporary stay on the regulation until the case, pending in the U.S. Court of Appeals for the District of Columbia Circuit, is resolved. The action is a setback for the rule’s supporters. The plan seeks to trim carbon emissions by 30% by 2030 and require states to develop plans to begin achieving reductions in 2020. Initial state plans are due in September.

The appeals court on Jan. 21 rejected the opponents’ request to block the rule. But the opponents—29 states, several utilities and industry groups—petitioned the Supreme Court on Jan. 28 to issue a stay.

The rule has many critics, but some states, renewable-energy companies and electric utilities have said they back the plan or have supported EPA in court as it defends the regulation.

The rule’s advocates say they are disappointed with the Supreme Court’s decision. Bob Perciasepe, president of the Center for Climate and Energy Solutions, said, “Whether or not the court ultimately upholds this particular rule, the need to cut carbon emissions will remain, and states need to figure out the most cost-effective ways to do that.”

Critics praised the high-court action. Mike Duncan—CEO of the American Coalition for Clean Coal Electricity, which includes coal and utility companies—said, “The stay is a signal the Supreme Court has serious concerns with the Clean Power Plan. We’re optimistic the [plan] will, ultimately, be rejected.” The appeals court’s decision is expected later this year.