Texas Transportation Code - TRANSP § 522.102. Implied Consent to Taking of Specimen

(a) A person who drives a commercial motor vehicle in this state is considered to have consented, subject to Chapter 724, to the taking of one or more specimens of the person's breath, blood, or urine for the purpose of analysis to determine the person's alcohol concentration or the presence in the person's body of a controlled substance or drug.

(b) Notwithstanding Chapter 724, one or more specimens may be taken at the request of a peace officer who, after stopping or detaining a person driving a commercial motor vehicle, has probable cause to believe that the person was driving the vehicle while having alcohol, a controlled substance, or a drug in the person's system.

(c) This section and Section 522.103 apply only to a person who is stopped or detained while driving a commercial motor vehicle.