A federal appeals court on Monday blocked the law firm Gibson, Dunn & Crutcher from filing a pro-Obamacare amicus brief because the submission would have caused the disqualification of an unidentified judge.

The U.S. Court of Appeals for the Fifth Circuit’s order pointed to a newly amended federal rule for appellate litigation and to a local court rule, both of which address circumstances where a court can reject an amicus brief if allowing it would force a judge to recuse.