40 ILCS 5/18-154
The State Comptroller in drawing warrants for salary on payroll vouchers certified by an employer shall draw such warrants for the salary specified, less the employee contribution to be deducted therefrom as certified in the payroll vouchers, and shall draw a warrant to this system for the total of the employee contributions so withheld. The warrant drawn to the system, together with the additional copy of the payroll supplied by the employer, shall be transmitted immediately to the secretary of the board.
The Comptroller shall draw warrants or prepare direct deposit transmittals upon the State Treasurer payable from the funds of this system for purposes provided in this Article upon the presentation of vouchers approved by the secretary in accordance with the resolutions of the board, and in the exercise of the investment authority, upon presentation of vouchers approved by the director of the Illinois State Board of Investment in accordance with the order and direction of said board.
40 ILCS 5/18-154