A person may not engage in picketing the purpose of which, directly or indirectly, is to secure the disregard or breach of a valid existing labor agreement arrived at between an employer and the representatives:

1. (1) designated by the employees for the purpose of collective bargaining; or
2. (2) certified as the bargaining unit under the National Labor Relations Act (29 U.S.C. Section 151 et seq.).

Acts 1993, 73rd Leg., ch. 269, Sec. 1, eff. Sept. 1, 1993.