220 ILCS 5/9-240
Except as in this Act otherwise provided, no public utility shall charge, demand, collect or receive a greater or less or different compensation for any product, or commodity furnished or to be furnished, or for any service rendered or to be rendered, than the rates or other charges applicable to such product or commodity or service as specified in its schedules on file and in effect at the time, except as provided in Section 9-104, nor shall any such public utility refund or remit, directly or indirectly, in any manner or by any device, any portion of the rates or other charges so specified, nor extend to any corporation or person any form of contract or agreement or any rule or regulation or any facility or privilege except such as are regularly and uniformly extended to all corporations and persons.
No law of the State shall be construed to prohibit a public utility from furnishing its service, product or commodity to its employees, officers, directors or pensioners, or its employees, officers, directors or pensioners from receiving such service, product or commodity, free or at rates or charges less than those specified in its filed schedules.
220 ILCS 5/9-240