Texas law does not authorize notaries public to certify an I-9 Form, and the Form itself does not contain a notarial certificate. Therefore, notaries should not notarize an I-9 Form. However, it is permissible for a notary public who is an employee of a business to assist that business in filling out the Form - as long as that work is not performed in the employee's capacity as a notary public, and as long as the employee does not place their notary seal on the document.
Source: Texas Secretary of State