The unidentified firm has asked the Supreme Court to block Mueller from obtaining records through a subpoena after a federal appeals court turned down the company's effort to block the court ordered release of documents. 

The identity of the firm and the foreign country at issue remain closely guarded secrets, but POLITICO first reported earlier this year that the dispute appeared to involve Mueller's prosecutors. A POLITICO reporter was in the D.C. Circuit Court of Appeals clerk's office in October when a person connected to the appeal arrived to request a copy of the special counsel's latest filing in the case.

When the case was argued at the D.C. Circuit last week, the courtroom was closed to the public. Court personnel went to unusual lengths to preserve the secrecy, ordering journalists to leave the floor where lawyers were presenting their positions. -Politico