The Commission and an employee organization certified as the exclusive representative of a bargaining unit shall execute a collective bargaining agreement incorporating all matters of agreement on wages, hours, and other terms and conditions of employment. If a collective bargaining agreement provides for a grievance procedure, that grievance procedure shall be the sole procedure for employees in the bargaining unit. The collective bargaining agreement may include an agency shop or other union security provision. The collective bargaining agreement supersedes any conflicting regulation or administrative policy of the Commission. A single–year or multiyear collective bargaining agreement shall expire at the close of the appropriate fiscal year. A collective bargaining agreement takes effect on the approval by the Commission and the membership of the union representing the bargaining unit. This section does not limit an employee’s right to an appeal to the Office of Administrative Hearings under § 18–123(b) of this title.