Indiana Code Title 34. Civil Law and Procedure § 34-14-1-11

Sec. 11. When declaratory relief is sought, all persons shall be made parties who have or claim any interest that would be affected by the declaration, and no declaration shall prejudice the rights of persons not parties to the proceeding.  In any proceeding in which a statute, ordinance, or franchise is alleged to be unconstitutional, the court shall certify this fact to the attorney general, and the attorney general shall be permitted to intervene for presentation of evidence, if evidence is otherwise admissible in the case, and for arguments on the question of constitutionality.  In any proceeding that involves the validity of a municipal ordinance or franchise, the municipality shall be made a party, and shall be entitled to be heard.  If the statute, ordinance, or franchise is alleged to be unconstitutional, the attorney general of the state shall also be served with a copy of the proceeding and be entitled to be heard.