A written proposal, invoice, or contract relating to plumbing services performed by or under the direction of a plumber licensed under this chapter must contain the name and license number of the responsible master plumber and the name, mailing address, and telephone number of the board. The person who performed the services shall give the customer an invoice or completed contract document on completion of the job, regardless of whether the person charged a fee for performing the services.
Tex. Occ. Code § 1301.302