29 CFR §18.614

1. (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.
2. (b)Interrogation by the judge. The judge may interrogate witnesses, whether called by the judge or by a party.
3. (c)Objections. Objections to the calling of witnesses by the judge or to interrogation by the judge must be timely.