Tex. Code Crim. Proc. art. 8.08

To suppress riots, unlawful assemblies and other disturbances at elections, any magistrate may appoint a sufficient number of special constables. Such appointments shall be made to each special constable, shall be in writing, dated and signed by the magistrate, and shall recite the purposes for which such appointment is made, and the length of time it is to continue. Before the same is delivered to such special constable, he shall take an oath before the magistrate to suppress, by lawful means, all riots, unlawful assemblies and breaches of the peace of which he may receive information, and to act impartially between all parties and persons interested in the result of the election.