29 C.F.R. § 18.614
Calling and interrogation of witnesses by judge
(a) Calling by the judge. The judge may, on the judge's own motion or at the suggestion of a party, call witnesses, and all parties are entitled to cross-examine witnesses thus called.
(b) Interrogation by the judge. The judge may interrogate witnesses, whether called by the judge or by a party.
(c) Objections. Objections to the calling of witnesses by the judge or to interrogation by the judge must be timely.