Texas Election Code - ELEC § 172.001. Nominating by Primary Election Required

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 must 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 20 percent or more of the total number of votes received by all candidates for governor in the election.