820 ILCS 156/25: Unlawful employer practices.

(a) It is unlawful for any employer to take any adverse action against an employee because the employee:

(1) exercises rights or attempts to exercise rights under this Act;

(2) opposes practices which such employee believes to be in violation of this Act; or

(3) supports the exercise of rights of another under this Act.

(b) Exercising rights under this Act includes:

(1) filing an action or instituting or causing to be instituted any proceeding under or related to this Act;

(2) providing or agreeing to provide any information in connection with any inquiry or proceeding relating to any right provided under this Act; or

(3) testifying to or agreeing to testify in any inquiry or proceeding relating to any right provided under this Act.