220 ILCS 5/10-110
At the time fixed for any hearing upon a complaint, the complainant and the person or corporation complained of, and such persons or corporations as the Commission may allow to intervene, shall be entitled to be heard and to introduce evidence. The Commission shall issue process to enforce the attendance of all necessary witnesses. At the conclusion of such hearing the Commission shall make and render findings concerning the subject matter and facts inquired into and enter its order based thereon. A copy of such order, certified under the seal of the Commission, shall be served upon the person or corporation complained of, or his or its attorney, which order shall, of its own force, take effect and become operative twenty days after the service thereof, except as otherwise provided, and shall continue in force either for a period which may be designated therein or until changed or abrogated by the Commission. Where an order cannot, in the judgment of the Commission, be complied with within twenty days, the Commission may prescribe such additional time as in its judgment is reasonably necessary to comply with the order, and may, on application and for good cause shown, extend the time for compliance fixed in its order. A full and complete record shall be preserved of all proceedings had before the Commission, or any member thereof, or any administrative law judge , on any formal hearing had, and all testimony shall be taken down by a stenographer appointed by the Commission, and the parties shall be entitled to be heard in person or by attorney.
In any proceeding involving a public utility in which the lawfulness of any of its rates or other charges shall be called in question by any person or corporation furnishing a commodity or service in competition with said public utility at prices or charges not subject to regulation, the Commission may investigate the competitive prices or other charges demanded or received by such person or corporation for such commodity or service, including the rates or other charges applicable to the transportation thereof. The Commission may, on its own motion or that of any party to such proceeding, issue subpoenas to secure the appearance of witnesses or the production of books, papers, accounts and documents necessary to ascertain the prices, rates or other charges for such commodity or service or for the transportation thereof, and shall dismiss from such proceeding any party failing to comply with a subpoena so issued.
In case of an appeal from any order or decision of the Commission, under the terms of Sections 10-201 and 10-202 of this Act, a transcript of such testimony, together with all exhibits or copies thereof introduced and all information secured by the Commission on its own initiative and considered by it in rendering its order or decision (and required by this Act to be made a part of its records) and of the pleadings, records and proceedings in the case, including transcripts of Commission meetings prepared in accordance with Section 10-102 of this Act, shall constitute the record of the Commission: Provided, that on appeal from an order or decision of the Commission, the person or corporation taking the appeal and the Commission may stipulate that a certain question or certain questions alone and a specified portion only of the evidence shall be certified to the court for its judgment, whereupon such stipulation and the question or questions and the evidence therein specified shall constitute the record on appeal.
Copies of all official documents and orders filed or deposited according to law in the office of the Commission, certified by the Chairman of the Commission or his or her designee to be true copies of the originals, under the official seal of the Commission, shall be evidence in like manner as the originals.
In any matter concerning which the Commission is authorized to hold a hearing, upon complaint or application or upon its own motion, notice shall be given to the public utility and to such other interested persons as the Commission shall deem necessary in the manner provided in Section 10-108, and the hearing shall be conducted in like manner as if complaint had been made to or by the Commission. But nothing in this Act shall be taken to limit or restrict the power of the Commission, summarily, of its own motion, with or without notice, to conduct any investigations or inquiries authorized by this Act, in such manner and by such means as it may deem proper, and to take such action as it may deem necessary in connection therewith. With respect to any rules, regulations, decisions or orders which the Commission is authorized to issue without a hearing, and so issues, any public utility or other person or corporation affected thereby and deeming such rules, regulations, decisions or orders, or any of them, improper, unreasonable or contrary to law, may apply for a hearing thereon, setting forth specifically in such application every ground of objection which the applicant desires to urge against such rule, regulation, decision or order. The Commission may, in its discretion, grant or deny the application, and a hearing, if had, shall be subject to the provisions of this and the preceding Sections.
220 ILCS 5/10-110