620 ILCS 5/53
All subpoenas issued under the laws of this State pertaining to aeronautics may be served by any person who is not a minor. The fees of witnesses for attendance and travel shall be the same as fees of witnesses before the circuit courts of this State, such fees to be paid at the time the witness is excused from further attendance, when the witness is subpoenaed at the instance of the Department, or any officer thereof, or any employee designated by it for the purpose of conducting any such investigation, inquiry or hearing; and the disbursements made in the payment of such fees shall be audited and paid in the same manner as are other expenses of the Department. Whenever a subpoena is issued at the instance of a complainant, respondent or other party to any proceeding before the Department, the Department may require that the cost of service thereof and the fee of the same shall be borne by the party at whose instance the witness is summoned before the Department, and the Department shall have power, in its discretion, to require a deposit to cover the cost of such service and witness fees and the payment of legal witness fees and mileage to the witness when served with subpoena. A subpoena issued as aforesaid shall be served in the same manner as a subpoena issued out of a court.
Any person who shall be served with a subpoena to appear and testify, or to produce books, papers, accounts or documents, either in person or by deposition, in the manner provided in this section, issued by the Department or by any officer thereof, or any employee thereof designated by it to conduct any such investigation, inquiry or hearing, in the course of an investigation, inquiry or hearing conducted under any of the provisions of the laws of this State pertaining to aeronautics, and who shall refuse or neglect to appear, or to testify, or to produce books, papers, accounts and documents relative to the investigation, inquiry or hearing as commanded in such subpoena, shall be guilty of a petty offense.
Any circuit court of this State, upon application of the Department, or an officer thereof, or an employee thereof designated by it for the purpose of conducting any such investigation, inquiry or hearing, may, in its discretion, compel the attendance of witnesses, the production of books, papers, accounts and documents, and the giving of testimony before the Department, or before any officer thereof, or any employee designated by it for the purpose of conducting any such investigation, inquiry or hearing, in person or by deposition, in the manner provided in this section, 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 thereof, or any employee thereof designated by it for the purpose of conducting any investigation, inquiry or hearing, or any party may, in any investigation, inquiry or hearing before the Department, or conducted under its authority, cause the deposition of witnesses residing within or without the State to be taken in the manner prescribed by law for taking like depositions in civil cases in courts of this State, and to that end may compel the attendance of witnesses and the production of papers, books, accounts and documents.
620 ILCS 5/53