Tex. Penal Code § 33.03

It is an affirmative defense to prosecution under Section 33.02 or 33.022 that the actor was an officer, employee, or agent of a communication common carrier or electric utility and committed the proscribed act or acts in the course of employment while engaged in an activity that is a necessary incident to the rendition of service or to the protection of the rights or property of the communication common carrier or electric utility.