§ 800. Boards of inquiry in labor disputes. Where any strike, lockout, or other labor dispute exists or is apprehended, the commissioner, for the purpose of inquiring into the causes and circumstances of the dispute may, if he thinks fit, refer any matters appearing to him to be connected with or relevant to the dispute to a board of inquiry appointed by him for the purpose of such reference; and the board shall, either in public or in private, at its discretion, and at any place within the state, inquire into the matters referred to it and report thereon to the commissioner. Provided, however, that no such reference shall be made unless and until there shall have been filed with the commissioner a certificate of the state board of mediation stating that in its opinion efforts to effect a voluntary settlement of the dispute have been unsuccessful.