Tex. Util. Code § 37.152
(a) Unless the commission issues a certificate that the present and future convenience and necessity will not be adversely affected, a certificate holder may not discontinue, reduce, or impair service to any part of the holder's certificated service area except for:
Acts 1997, 75th Leg., ch. 166, Sec. 1, eff. Sept. 1, 1997.