Ill. Admin. Code tit. 80 § 1240.180
Parties may file a motion with the Board to request leave to file an amicus curiae brief or the Board, on its own motion, may solicit such briefs. The Board's standards by which to grant leave to file an amicus curiae brief will include the importance of the issue presented, the general application of the issue presented and the need perceived by the Board for additional briefing on the issue presented. The amicus curiae brief shall conform to any conditions imposed by the Board for briefs in the case in which the brief is filed. Amicus curiae parties may be invited to participate in oral arguments heard by the Board. The Board will accept amicus curiae briefs in its proceedings. The filing of such briefs shall not serve to postpone or delay the proceedings.
Ill. Admin. Code tit. 80, § 1240.180