40 ILCS 5/18-155
Each employer, in preparing payroll vouchers shall indicate, in addition to other things: (1) the amount of contributions specified to be deducted from the salary or wages of each participant included in the voucher; (2) the net amount payable to each participant after the deduction of such contribution; and (3) the total of all participant contributions so deducted. An additional certified copy of each payroll voucher certified by the State shall be prepared and forwarded together with the original payroll voucher to the State Comptroller for transmittal to the board.
Each employer other than the State, in drawing warrants for items of salary payable to participants, shall draw such warrants for the salary specified less the participant contribution to be deducted therefrom as certified in the payroll vouchers and shall draw a warrant to this system for the total of the participant 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.
40 ILCS 5/18-155