Texas Utilities Code - UTIL § 36.004. Equality of Rates and Services

(a) An electric utility may not directly or indirectly charge, demand, or receive from a person a greater or lesser compensation for a service provided or to be provided by the utility than the compensation prescribed by the applicable tariff filed under Section 32.101.

(b) A person may not knowingly receive or accept a service from an electric utility for a compensation greater or less than the compensation prescribed by the tariff.

(c) Notwithstanding Subsections (a) and (b), an electric utility may charge an individual customer for wholesale or retail electric service in accordance with Section 36.007.

(d) This title does not prevent a cooperative corporation from returning to its members net earnings resulting from its operations in proportion to the members' purchases from or through the corporation.