35 ILCS 635/27.5
Every telecommunications retailer under this Act shall keep books, records, papers, and other documents that are adequate to reflect the information which such telecommunications retailers are required by this Act to report to the Department by filing monthly returns with the Department. All books and records and other papers and documents required by this Act to be kept shall be kept in the English language and shall, at all times during business hours of the day, be subject to inspection by the Department or its duly authorized agents and employees. Books and records reflecting gross charges received during any period with respect to which the Department is authorized to establish liability as provided by this Act shall be preserved until the expiration of such period unless the Department, in writing, authorizes their destruction or disposal at an earlier date.
The Department may, upon written authorization of the Director, destroy any returns or any records, papers, or memoranda pertaining to such returns upon the expiration of any period covered by such returns with respect to which the Department is authorized to establish liability.
35 ILCS 635/27.5