(a) Witnesses at the hearing shall testify under oath or affirmation. The administrative law judge may examine the witnesses and shall allow the parties or their representatives to do so.

(b) No person shall be required to attend as a witness in any proceeding before an administrative law judge at a place more than 100 miles from his place of residence, unless his lawful mileage and fees for one day's attendance shall be paid or tendered to him in advance of the hearing date.