Tex. Bus. Orgs. Code § 21.362

Except as provided by the corporation's certificate of formation, a shareholder of a corporation incorporated before September 1, 2003, has the right to cumulatively vote the number of shares the shareholder owns in the election of directors to the extent permitted and in the manner provided by Section 21.361. A corporation may limit or deny a shareholder's right to cumulatively vote shares at any time after September 1, 2003, by amending its certificate of formation.