Ill. Admin. Code tit. 50, § 2402.120 – Intervention

a) Upon timely written application, the Hearing Officer shall permit any party to intervene in a hearing proceeding, subject to the necessity for conducting an orderly and expeditious hearing, when either of the following conditions is met:
1. 1) when the party is so situated that he may be adversely affected by a final order arising from the hearing; or
2. 2) when a party's circumstances and the hearing proceeding have a question of law or fact in common.
b) Two copies of a petition for intervention shall be filed with the Department (one for the Department attorney and one for the Hearing Officer) and one copy served on each additional party no later than 48 hours prior to the date set for hearing of the matters set forth in the Notice of Hearing. The Hearing Officer may permit later intervention when there is good cause for the delay.
c) An intervenor shall have all the rights of an original party, except that the Hearing Officer may, in his Order allowing intervention, provide that the applicant shall be bound by Orders theretofore entered or by evidence theretofore received, that the applicant shall not raise issues which might more properly have been raised at an earlier stage of the proceeding, that the applicant shall not raise new issues or add new parties, or that in other respects the applicant shall not interfere with the control of the Hearing, as justice and the avoidance of undue delay may require.