Government Code §824.005

(a) A person who has retired under the retirement system may revoke that retirement by filing with the system a written revocation in a form prescribed by the system. For a revocation to be effective, the retirement system must receive the written revocation before the later of the due date for the first payment of the annuity or the date on which the retirement system makes the first payment. After the later of those dates, a retiree may not revoke the retirement. For purposes of this subtitle, the retirement system makes a payment by depositing a check in the mail or sending payment by electronic fund transfer. (b) A person who has retired under the retirement system revokes that retirement if the person becomes employed in any position in a public school during the first month following that person's effective date of retirement, or during the first two months following an effective date of retirement established by reliance on Section 824.002 (d), and must return any retirement benefits received under the original retirement. (c) A person who revokes a retirement under this section is restored to membership in the retirement system as if that person had never retired.