Texas Tax Code - TAX § 111.023. Written Authorization

(a) The comptroller may require that a report, return, declaration, claim for refund, or other document that is required or permitted to be filed with the comptroller and that is submitted by an attorney, accountant, or other representative of a taxpayer on behalf of the taxpayer be accompanied by express written authorization of the taxpayer in whose name or on whose behalf it is purportedly submitted.

(b) An officer, director, or employee of the taxpayer whose duties include administering the taxpayer's rights and responsibilities with the comptroller may sign the written authorization.  The authorization must include the title and telephone number of the officer, director, or employee who signs the authorization for verification by the comptroller.

(c) The comptroller may impose a requirement of Subsection (b) on a taxpayer's assignment of a claim for refund.