65 ILCS 5/10-4-4
In municipalities of more than 500,000, the corporate authorities may investigate the enforcement of the municipal ordinances, rules and regulations, and the action, conduct and efficiency of all officers, agents and employees of the municipality. In the conduct of such investigations the corporate authorities may hold public hearings. Each member of the corporate authorities shall have power to administer oaths, and the clerk of the municipality, by order of the corporate authorities, shall issue subpoenas to secure the attendance and testimony of witnesses and the production of books and papers relevant to such investigations and to any hearing before the corporate authorities or any member thereof.
Any circuit court of this state upon application of the corporate authorities, or any member thereof, may in its discretion compel the attendance of witnesses, the production of books and papers, and the giving of testimony before the corporate authorities or any member thereof, by attachment for contempt or otherwise in the same manner as the production of evidence may be compelled before the court.
65 ILCS 5/10-4-4