(a) Before making such order, the department shall hold a public hearing, or hearings, at which an opportunity to be heard shall be afforded to any employer or representative of employers, and any home-worker or representative of home-workers, and any other person or persons having an interest in the subject matter of hearing. A public notice of such hearing shall be given in such manner as may be fixed by the department. Such notice shall be made at least thirty days before the hearing is held. Such hearing, or hearings, shall be in such place, or places, as the department deems most convenient to the employers and home-workers to be affected by such order.

(b) The department shall determine the effective date of such order, which date shall be not less than ninety days after the date of the promulgation of its order. The order shall set forth the type or types of manufacturing which are prohibited after its effective date.