Tex. Loc. Gov't Code § 43.0698

If a petition protesting the annexation of an area under this subchapter is signed by a number of registered voters of the municipality proposing the annexation equal to at least 50 percent of the number of voters who voted in the most recent municipal election and is received by the secretary of the municipality before the date the election required by this subchapter is held, the municipality may not complete the annexation of the area without approval of a majority of the voters of the municipality voting at a separate election called and held for that purpose.