Texas Election Code - ELEC § 172.002. Nominating by Primary Election Authorized

(a) Except as otherwise provided by this code, a political party's nominees in the general election for offices of state and county government and the United States Congress may be nominated by primary election, held as provided by this code, if the party's nominee for governor in the most recent gubernatorial general election received at least two percent but less than 20 percent of the total number of votes received by all candidates for governor in the election.

(b) If any nominee of a party is nominated by primary election, none of that party's nominees may be nominated that year by convention.

(c) For a political party to be entitled to hold a primary election under this section, the state chair, not later than one year before general election day, must deliver written notice to the secretary of state that the party will hold a primary election in the general election year.