Tex. R. Civ. P. 254
In all civil actions, including matters of probate, and in all matters ancillary to such suits which require action by or the attendance of an attorney, including appeals but excluding temporary restraining orders, at any time within thirty days of a date when the legislature is to be in session, or at any time the legislature is in session, or when the legislature sits as a Constitutional Convention, it shall be mandatory that the court continue the cause if it shall appear to the court, by affidavit, that any party applying for continuance, or any attorney for any party to the cause, is a member of either branch of the legislature, and will be or is in actual attendance on a session of the same. If the member of the legislature is an attorney for a party to the cause, his affidavit shall contain a declaration that it is his intention to participate actively in the preparation and/or presentation of the case. Where a party to any cause, or an attorney for any party to a cause, is a member of the legislature, his affidavit need not be corroborated. On the filing of such affidavit, the court shall continue the cause until thirty days after adjournment of the legislature and the affidavit shall be proof of the necessity for the continuance, and the continuance shall be deemed one of right and shall not be charged against the movant upon any subsequent application for continuance.The right to a continuance shall be mandatory, except only where the attorney was employed within ten days of the date the suit is set for trial, the right to continuance shall be discretionary.
Tex. R. Civ. P. 254