An employing unit or employer association that wishes to participate in the work sharing unemployment insurance program shall submit to the Secretary a written work sharing plan that the employing unit or representative of the employer association has signed. Within 15 days after receipt of a work sharing plan, the Secretary shall give written approval or disapproval of the plan. A decision by the Secretary to disapprove a work sharing plan shall identify the reasons for the disapproval. When the Secretary disapproves a work sharing plan, the decision is final and may not be appealed. After 15 days after the Secretary disapproves a work sharing plan, the employing unit or employer association may submit a new work sharing plan.