Section 94. The commissioner and his duly authorized assistants shall have authority to enforce sections eighty-four to one hundred and one, inclusive, and to prosecute all violations thereof. Before any prosecution is begun by said commissioner or any of his duly authorized assistants, the parties concerned shall be given an opportunity to be heard before said commissioner or a person designated by him for such purpose. The parties concerned shall be given reasonable notice of the hearing, specifying the day, hour and place thereof, and accompanied by a description of the alleged violation.