The Labor Commissioner, with the advice and approval of said board, shall appoint at least five mediators to act for it in making investigations and adjusting labor disputes. Each such mediator shall, with the approval of said board, expressly granted in each case in which he is required to function, have all the powers of a member of said board to enter establishments, to examine payrolls or other records, to issue subpoenas and to administer oaths. In any civil or criminal case, any preliminary proceeding to such case, or any legislative or administrative proceeding, any person acting as a mediator under this chapter shall not disclose any confidential communication made to him in the course of his mediation duties unless the party making such communication waives such privilege. Said commissioner shall assign such stenographic and other clerical assistants to said board as may be necessary in the performance of its duties. All records of hearings and other proceedings of said board shall be kept on file in the Labor Department.