820 ILCS 45/2
No employer who makes available to employees group health insurance coverage or otherwise provides for payment of or furnishes medical or health care services under a group health insurance policy or contract, non-profit health care service plan contract, health maintenance organization or other subscriber contract, or any other health care plan or arrangement which pays for or furnishes medical or health care services by a provider of such services, whether by insurance or not, shall discharge an employee where the basis for such discharge is retaliation for the filing of a legitimate claim or the actual use or receipt of medical or health care services by an employee under such insurance policy or contract, or any other health care plan or arrangement, whether insurance or not.
820 ILCS 45/2