The Labor Commissioner is authorized to investigate the wages, hours of employment, necessary expense of living and health, so far as affected by their employment, of wage-earning persons in stores, wholesale and retail, public utilities, photographic, undertaking, millinery and dressmakers’ establishments, hotels, restaurants, laundries, hairdressing and barber shops, domestic service, manufacturing establishments and tenement house work. Such investigation shall be conducted under the supervision of said commissioner by a person specially trained for this work and selected by him. Other employees of said bureau may be detailed to assist in the prosecution of such investigation. Said commissioner shall have power to demand from those possessed of it such information as is pertinent to the investigation herein authorized, and any person who refuses to furnish the information so demanded, within a reasonable time, shall be fined not more than one hundred dollars. The commissioner may employ special agents to assist him in his investigations. Such agents shall receive compensation for the time actually employed in such service.