35 ILCS 135/18
The Department or any officer or employee of the Department designated, in writing, by the Director thereof, shall at its or his or her own instance, or on the written request of any interested party to the proceeding issue subpoenas requiring the attendance of and the giving of testimony by witnesses, and subpoenas duces tecum requiring the production of books, papers, records or memoranda. All subpoenas and subpoenas duces tecum issued under the terms of this Act may be served by any person of full age. The fees of witnesses for attendance and travel shall be the same as the fees of witnesses before the circuit court of this State; such fees to be paid when the witness is excused from further attendance. When the witness is subpoenaed at the instance of the Department or any officer or employee thereof, such fees shall be paid in the same manner as other expenses of the Department, and when the witness is subpoenaed at the instance of any other party to any such proceeding, the cost of service of the subpoena or subpoena duces tecum and the fee of the witness shall be borne by the party at whose instance the witness is summoned. In such case the Department, in its discretion, may require a deposit to cover the cost of such service and witness fees. A subpoena or subpoena duces tecum so issued shall be served in the same manner as a subpoena or subpoena duces tecum issued out of a court.
Any circuit court of this State, upon the application of the Department or any officer or employee thereof, or upon the application of any other party to the proceeding, may, in its or his discretion, compel the attendance of witnesses, the production of books, papers, records or memoranda and the giving of testimony before the Department or any officer or employee thereof conducting an investigation or holding a hearing authorized by this Act, by an attachment for contempt, or otherwise, in the same manner as production of evidence may be compelled before the court.
The Department or any officer or employee thereof, or any other party in an investigation or hearing before the Department, may cause the depositions of witnesses within the State to be taken in the manner prescribed by law for like depositions, or depositions for discovery in civil actions in courts of this State, and to that end compel the attendance of witnesses and the production of books, papers, records or memoranda, in the same manner hereinbefore provided.
35 ILCS 135/18