735 ILCS 5/2-1101
The clerk of any court in which an action is pending shall, from time to time, issue subpoenas for those witnesses and to those counties in the State as may be required by either party. Every clerk who shall refuse so to do shall be guilty of a petty offense and fined any sum not to exceed $100. An attorney admitted to practice in the State of Illinois, as an officer of the court, may also issue subpoenas on behalf of the court for witnesses and to counties in a pending action. An order of court is not required to obtain the issuance by the clerk or by an attorney of a subpoena duces tecum. For good cause shown, the court on motion may quash or modify any subpoena or, in the case of a subpoena duces tecum, condition the denial of the motion upon payment in advance by the person in whose behalf the subpoena is issued of the reasonable expense of producing any item therein specified.
In the event that a party has subpoenaed an expert witness including, but not limited to physicians or medical providers, and the expert witness appears in court, and a conflict arises between the party subpoenaing the expert witness and the expert witness over the fees charged by the expert witness, the trial court shall be advised of the conflict. The trial court shall conduct a hearing subsequent to the testimony of the expert witness and shall determine the reasonable fee to be paid to the expert witness.
735 ILCS 5/2-1101