In an unusual move, the U.S. Department of Justice has filed a brief with the U.S. Supreme Court opposing a request for the high court to hear an appeal of a blockbuster American Express Co. antitrust case. The DOJ, under the Obama administration, had brought the case along with a group of states.

While it may not be unusual for one administration's Justice Department to opt out of a case that was brought under a previous attorney general, it is rare for the DOJ to openly and actively oppose the granting of cert in its own case.

Randy Stutz, associate general counsel at the American Antitrust Institute, said he has seen a private plaintiff choose to opt out of an appeal, but he has never seen the federal government oppose cert in its own case. The institute has not taken a position on the litigation , Stutz said, “but it certainly is a unique situation.”