820 ILCS 96/1-40
Notwithstanding any other law to the contrary, any agreement, clause, covenant, or waiver, settlement agreement, or termination agreement that waives the right of an employee, prospective employee, or former employee to testify in an administrative, legislative, or judicial proceeding concerning alleged criminal conduct or alleged unlawful employment practices on the part of the other party to the employment contract, settlement agreement, or termination agreement, or on the part of the party's agents or employees, when the employee, prospective employee, or former employee has been required or requested to attend the proceeding pursuant to a court order, subpoena, or written request from an administrative agency or the legislature, is void and unenforceable under the public policy of this State. This Section is declarative of existing law.
820 ILCS 96/1-40