The U.S. Court of Appeals for the D.C. Circuit on Monday surprised both sides in the closely watched Clean Power Plan case by deciding to have a full panel of the active circuit judges hear the case – and to postpone the hearing to Sept. 27.

Though the circuit court move delays an initial hearing for another four months, in the end a decision by the entire panel of active judges could speed up the appellate process, exclude some of the most conservative judges who are on senior status, and guard against the possibility of gridlock at the Supreme Court where a tie 4-4 vote would leave the appellate court decision intact.

The court’s move is extremely unusual, but is permitted under its procedural rules when a case “involves a question of exceptional importance.”

It is also a recognition of the political sensitivity of the case, in which about two dozen state attorneys general are asking the court to throw out one of President Barack Obama’s main tools in his fight against greenhouse gas emissions.

The plan, proposed by the Environmental Protection Agency, would set guidelines for states to reduce greenhouse gas emissions and would reduce carbon pollution from existing power plants by 32 percent below 2005 levels by 2030.

The lawsuit, which pits a host of states and industry groups against the government and its own dense coterie of state and environmentalist supporters, was scheduled to be heard by a three judge panel on June 2. Even if the D.C. Circuit court had stuck with that plan, it would have been possible for the losing side to ask for a full panel of judges, known as en banc, to hear and reconsider the case.

David Doniger, director of the climate and clean air program at the Natural Resources Defense Council, said that “the court’s order may well speed up final resolution of the case. We look forward to our day in court.”

Hearings by the full circuit include only active judges. Judges who have taken senior status in the case include conservatives like David B. Sentelle and Laurence H. Silberman. Two judges appointed by Democrats, Cornelia T.L. Pillard and Obama’s Supreme Court nominee Merrick B. Garland, also recused themselves from the case. Garland is trying to win a confirmation hearing in the Senate and Pillard gave no reason. The remaining panel will include five judges appointed by Democrats and four appointed by Republicans.

Tomas Carbonell, director of regulatory policy at the Environmental Defense Fund, which is a party to the case, said that the order for an en banc hearing “will enable the full D.C. Circuit to resolve the legal challenges to the Clean Power Plan immediately and without delay – an especially important development given the urgent threat of climate change to the health and security of communities and families across our nation.”

The circuit court’s order for a full panel of active judges is the latest in a series of unusual steps regarding the case. The Supreme Court issued a stay, freezing implementation of the plan until the courts decide. Such measures are rarely taken before the case even reaches the Supreme Court.

“When it comes to the Clean Power Plan, it is best to expect the unexpected,” said Scott Segal, director of the Electric Reliability Coordinating Council, an industry group. Segal is also a partner at the law firm Bracewell where he has represented utilities and coal companies.

Segal interpreted the order to have a full panel hear the case as a setback for EPA defenders who say the plan falls squarely within the agency’s regulatory power. He said they “have portrayed the case as essentially a garden-variety administrative law case that can be disposed of by simply citing to agency deference. It would appear the D.C. Circuit sees it differently.”

(c) 2016, The Washington Post · Steven Mufson