Ill. Admin. Code tit. 92 § 454.600
Parties participating in hearings conducted under these Rules may obtain discovery pursuant to this Rule regarding any matter not privileged, which is relevant to the subject matter involved in the pending proceeding or appears reasonably calculated to lead to the discovery of admissible evidence; provided that discovery may be had only when the presiding officer, upon his own motion or upon a petition filed by a party, and upon good cause shown, shall have entered an order approving such use. Such petitions must be filed in sufficient time to allow for the filing of replies and for consideration by the presiding officer without requiring the postponement of any established date for hearing.
Ill. Admin. Code tit. 92, § 454.600
Amended at 5 Ill. Reg. 12989, effective November 16, 1981