Tex. Civil Practice and Remedies Code § 37.006: PARTIES.

(a) When declaratory relief is sought, all persons who have or claim any interest that would be affected by the declaration must be made parties. A declaration does not prejudice the rights of a person not a party to the proceeding.

(b) In any proceeding that involves the validity of a municipal ordinance or franchise, the municipality must be made a party and is entitled to be heard, and if the statute, ordinance, or franchise is alleged to be unconstitutional, the attorney general of the state must also be served with a copy of the proceeding and is entitled to be heard.

Acts 1985, 69th Leg., ch. 959, Sec. 1, eff. Sept. 1, 1985.