220 ILCS 5/4-202
Whenever the Commission shall be of the opinion that any public utility is failing or omitting or about to fail or omit to do anything required of it by law or by any order, decision, rule, regulation, direction, or requirement of the Commission, issued or made under authority of this Act, or is doing anything or about to do anything or permitting anything or about to permit anything to be done contrary to or in violation of law or any order, decision, rule, regulation, direction, or requirement of the Commission, issued or made under authority of this Act, the Commission shall file an action or proceeding in the circuit court in and for the county in which the case or some part thereof arose, or in which the person or corporation complained of, if any, has its principal place of business, or in which the person complained of, if any, resides, in the name of the People of the State of Illinois, for the purpose of having the violation or threatened violation stopped and prevented, either by mandamus or injunction.
The Commission may express its opinion in a resolution based upon whatever facts and evidence have come to its attention and may issue the resolution ex parte and without holding any administrative hearing before bringing suit. Except in cases involving an imminent threat to the public health or public safety, no such resolution shall be adopted until 48 hours after the public utility has been given notice of (i) the substance of the alleged violation, including a citation to the law or order, decision, rule, regulation, or direction of the Commission alleged to have been violated and (ii) the time and date of the meeting at which such resolution will first be before the Commission for consideration.
The Commission shall file the action or proceeding by complaint in the circuit court alleging the violation or threatened violation complained of and praying for appropriate relief by way of mandamus or injunction. It shall thereupon be the duty of the court to specify a time, not exceeding 20 days after the service of the copy of the complaint, within which the public utility complained of must answer the complaint, and in the meantime said public utility may be restrained. In case of default in answer, or after answer, the court shall immediately inquire into the facts and circumstances of the case. Such corporation or persons as the court may deem necessary or proper to be joined as parties, in order to make its judgment or order effective, may be joined as parties. The final judgment in any action or proceeding shall either dismiss the action or proceeding or grant relief by mandamus or injunction or be made permanent as prayed for in the complaint, or in such modified or other form as will afford appropriate relief. An appeal may be taken from such final judgment as in other civil cases.
220 ILCS 5/4-202