220 ILCS 5/17-400

Conditions prohibiting municipal system participation. At no time shall a municipal system make an election under Sections 17-200 or 17-300 of this Article if such election places at risk:

(1) Any status held by the municipal system or municipal corporation or political subdivision which provides exemption from State or federal tax statutes; or

(2) Any debt, credit instrument or other contractual financial obligation held by, or on behalf of the municipal system which was entered into under an exemption from State or federal tax statutes.