Section 5A. In all investigations and inquiries authorized by law to be made by the department and in all proceedings before it, any commissioner of the department may summon witnesses, administer oaths and take testimony. The fees of such witnesses for attendance and travel shall be the same as for witnesses before the superior court and shall be paid by the commonwealth upon the certificate of the department filed with the comptroller. The fees of such witnesses need not be paid or tendered to them prior to their attendance and testimony. Subpoenas may be issued at the instance of a complainant, respondent or any other party to any proceeding before the commission under such rules as the department may establish, in which case the cost of service and the fees of witnesses shall be borne by the party at whose instance the witness is summoned, and such fees shall be paid to the witnesses as provided in the case of witnesses before the superior court.