The U.S. Supreme Court has blocked implementation of President Obama’s signature plan to address climate change pending a decision by the D.C. Circuit Court of Appeals on the plan’s legality. The Clean Power Plan is being challenged by 29 states and dozens of corporations and industry groups. The decision is a bit of a slap in the face to the D.C. Circuit, which denied the request to stay the regulation less than a month ago. The Supreme Court’s action is unprecedented: It’s the first time it has ever blocked implementation of an environmental regulation before the D.C. Circuit has had a chance to consider the regulation on its merits.