An entire floor at the U.S. Court of Appeals for the D.C. Circuit was locked down Friday as judges heard arguments in a sealed case involving a grand jury subpoena that's believed to be linked to the special counsel's investigation.

The lockdown came as a three-judge panel considers a case arising out of a grand jury subpoena fight, suspected to be linked to Robert Mueller's special counsel investigation into Russian interference in the 2016 presidential election. Details about the case—particularly the identity of the party hoping to suppress the subpoena—have been held under wraps.

Judges Thomas Griffith, David Tatel and Stephen Williams heard two other lawsuits Friday morning: one suit addressing the president's financial disclosure reporting requirements and another revolving around individuals who've participated in an annual diversity visa lottery. Once those arguments drew to a close an hour later, court security officers announced a recess and promptly ushered the audience out. Only law clerks were permitted to stay.