Tex. R. Civ. P. 12
A party in a suit or proceeding pending in a court of this state may, by sworn written motion stating that he believes the suit or proceeding is being prosecuted or defended without authority, cause the attorney to be cited to appear before the court and show his authority to act. The notice of the motion shall be served upon the challenged attorney at least ten days before the hearing on the motion. At the hearing on the motion, the burden of proof shall be upon the challenged attorney to show sufficient authority to prosecute or defend the suit on behalf of the other party. Upon his failure to show such authority, the court shall refuse to permit the attorney to appear in the cause, and shall strike the pleadings if no person who is authorized to prosecute or defend appears. The motion may be heard and determined at any time before the parties have announced ready for trial, but the trial shall not be unnecessarily continued or delayed for the hearing.
Tex. R. Civ. P. 12