Texas Constitution art. 3 §18

No Senator or Representative shall, during the term for which he was elected, be eligible to (1) any civil office of profit under this State which shall have been created, or the emoluments of which may have been increased, during such term, or (2) any office or place, the appointment to which may be made, in whole or in part, by either branch of the Legislature; provided, however, the fact that the term of office of Senators and Representatives does not end precisely on the last day of December but extends a few days into January of the succeeding year shall be considered as de minimis, and the ineligibility herein created shall terminate on the last day in December of the last full calendar year of the term for which he was elected. No member of either House shall vote for any other member for any office whatever, which may be filled by a vote of the Legislature, except in such cases as are in this Constitution provided, nor shall any member of the Legislature be interested, either directly or indirectly, in any contract with the State, or any county thereof, authorized by any law passed during the term for which he was elected. (Feb. 15, 1876. Amended Nov. 5, 1968.)