Mo. Rev. Stat. § 527.020: Power to construe.

Any person interested under a deed, will, written contract or other writings constituting a contract, or whose rights, status or other legal relations are affected by a statute, municipal ordinance, contract or franchise, may have determined any question of construction or validity arising under the instrument, statute, ordinance, contract, or franchise and obtain a declaration of rights, status or other legal relations thereunder.