Texas Election Code - ELEC § 233.004. Intervention

(a) The court may permit one or more qualified voters of the territory covered by the contested election to intervene as contestants or contestees.

(b) The court shall determine the extent to which each intervenor may participate in the contest as the ends of justice and orderly procedure require.  However, the court must permit at least one intervention on the side of the contestee, if requested to do so, and must permit the intervening contestee to participate fully in the conduct of the contest.