Tex. Rev. Civ. Stat. art. 3863

The said Commission shall have authority, and it shall be its duty to call upon such express companies for reports, and investigate their books in the same manner as may be prescribed by law for the regulation of railroad companies, and the said Commission shall have power and authority to institute suits, sue out such writs and process as may be applicable and authorized for the regulation of railroad companies. All laws, rules and regulations made and prescribed for the government and control of railroads, when applicable, shall be of equal force and effect as to express companies.