When any controversy shall arise between employer and employee as to wages, hours of employment, or working or living conditions, in any industry not hereinbefore specified, the parties to such controversy may, by mutual agreement, and with the consent of the secretary of labor, refer the same to the secretary for findings and orders. Such agreement of reference shall be in writing, signed by the parties thereto; whereupon the secretary shall proceed to investigate, hear, and determine the controversy as in other cases, and in such case the findings and orders of the secretary as to the controversy shall have the same force and effect as though made in any essential industry as herein provided.