Tex. Spec. Dist. Local Laws Code § 1061.304

An election to adopt, change the rate of, or abolish a tax authorized by this subchapter is called by the adoption of an order of the board. The board may call an election on its own motion and shall call an election if a number of qualified voters in the district equal to at least five percent of the number of registered voters in the district petitions the board to call the election.