A U.S. regulatory agency has filed a sealed appeal challenging a Chicago judge who initiated a sanctions investigation last month focused on whether federal officials violated the terms of a settlement that barred the government from making certain public statements about the deal.

The new case in the U.S. Court of Appeals for the Seventh Circuit is under seal, and officials at the U.S. Commodity Futures Trading Commission declined to comment Monday about what arguments the agency is making and what action it wants the appeals panel to take.