35 ILCS 615/12b

The Department shall not take any action in law or administratively against a municipally owned defendant for monies, interest or penalties claimed because such defendant has failed to include in its gross receipts amounts due under this Act which, in order to be exempt from taxation, should have been billed to its customers separately as a charge for reimbursement of taxes, but were not so billed, provided such defendant, in fact, included such amounts in its bills to its customers and informed such customers of the nature of the included amounts.