Texas Election Code - ELEC § 202.004. Nomination by Primary Election

(a) A political party's nominee for an unexpired term must be nominated by primary election if:

(b) If the vacancy occurs on or before the 10th day before the date of the regular deadline for candidates to file applications for a place on the general primary ballot, an application for the unexpired term must be filed by the regular filing deadline.

(c) If the vacancy occurs after the 10th day before the date of the regular filing deadline, an application for the unexpired term must be filed not later than 6 p.m. of the fifth day after the date of the regular filing deadline.

(d) The filing fee or petition requirements for a candidate for an unexpired term are the same as for a candidate for a full term.