Tex. Gov't Code § 659.021

The administrative head of a state agency as defined by Section 658.001 whose salary as administrative head is established by the General Appropriations Act may not receive a salary higher than that established salary, even if the administrative head performs duties assigned to a position title classified in the state's position classification plan that is assigned to a salary group that would pay a higher salary, unless the General Appropriations Act specifically provides that a higher salary may be received.