5 ILCS 365/9

Any authorization to withhold from the salary, wages or annuity of an employee or annuitant shall terminate and such withholding shall cease upon the happening of any of the following events: (1) termination of employment or termination of payment of an annuity, as the case may be; (2) written notice by the employee or annuitant of cancellation of such former authorization, except that an authorization to withhold for the payment of optional contributions to a retirement system through an employer pickup is irrevocable; (3) expiration of the time during which such withholding was authorized; (4) when the total amount authorized to be withheld has been so withheld.