220 ILCS 5/10-101
The Commission, or any commissioner or administrative law judge designated by the Commission, shall have power to hold investigations, inquiries and hearings concerning any matters covered by the provisions of this Act, or by any other Acts relating to public utilities subject to such rules and regulations as the Commission may establish. In the conduct of any investigation, inquiry or hearing the provisions of the Illinois Administrative Procedure Act, including but not limited to Sections 10-25 and 10-35 of that Act, shall be applicable and the Commission's rules shall be consistent therewith. Complaint cases initiated pursuant to any Section of this Act, investigative proceedings and ratemaking cases shall be considered "contested cases" as defined in Section 1-30 of the Illinois Administrative Procedure Act, any contrary provision therein notwithstanding. Any proceeding intended to lead to the establishment of policies, practices, rules or programs applicable to more than one utility may, in the Commission's discretion, be conducted pursuant to either rulemaking or contested case provisions, provided such choice is clearly indicated at the beginning of such proceeding and subsequently adhered to. No violation of this Section or the Illinois Administrative Procedure Act and no informality in any proceeding or in the manner of taking testimony before the Commission, any commissioner or administrative law judge of the Commission shall invalidate any order, decision, rule or regulation made, approved, or confirmed by the Commission in the absence of prejudice. All hearings conducted by the Commission shall be open to the public.
Each commissioner and every administrative law judge of the Commission designated by it to hold any inquiry, investigation or hearing, shall have the power to administer oaths and affirmations, certify to all official acts, issue subpoenas, compel the attendance and testimony of witnesses, and the production of papers, books, accounts and documents.
Hearings shall be held either by the Commission or by one or more commissioners or administrative law judges .
When any attorney who is not admitted to the practice of law in Illinois by unlimited or conditional admission, but who is licensed in another state, territory, or commonwealth of the United States, the District of Columbia, or a foreign country may desire to appear before the Commission, such attorney shall be allowed to appear before the Commission as provided in Supreme Court Rule 707.
All evidence presented at hearings held by the Commission or under its authority shall become a part of the records of the Commission. In all cases in which the Commission bases any action on reports of investigation or inquiries not conducted as hearings, such reports shall be made a part of the records of the Commission. All proceedings of the Commission and all documents and records in its possession shall be public records, except as in this Act otherwise provided.
To the extent consistent with this Section and the Illinois Administrative Procedure Act, the Commission may adopt reasonable and proper rules and regulations relative to the exercise of its powers, and proper rules to govern its proceedings, and regulate the mode and manner of all investigations and hearings, and alter and amend the same.
220 ILCS 5/10-101