40 ILCS 5/14-104.4
For purposes of this Article, the term "award for back pay under a statute" means an award, determination or agreement granted or approved by a court or administrative agency which arises under a State or federal law protecting an employee's right to employment or wages, and which provides for payment by the employer for a period of deemed employment for which the employee has not already established service credit.
Membership service credit will be retroactively granted pursuant to an "award for back pay under a statute" for the time period during which the service was deemed to have been performed. Employee contributions will be deducted at the applicable rates in effect for the time periods involved. The employer's share of retirement contributions will be paid at the current Board rate in effect at the time of payment.
40 ILCS 5/14-104.4