Haven't found tie-in between Loop and Illinois pensions but I'm sure it's in there. Meanwhile there's this:

Illinois constitution prohibits default on public pensions. Taxpayers on the hook for shortfalls.

http:// www.ilga.gov/commission/lrb/con13.htm

SECTION 5. PENSION AND RETIREMENT RIGHTS

Membership in any pension or retirement system of the

State, any unit of local government or school district, or

any agency or instrumentality thereof, shall be an

enforceable contractual relationship, the benefits of which

shall not be diminished or impaired.

(Source: Illinois Constitution.)