On December 13, five candidates for citywide non-partisan Chicago office filed a federal lawsuit, alleging that the requirement that they each collect 12,500 valid signatures is unconstitutional.  The case is Stone v Neal, 10cv-7727.  Here is the complaint.

The lawsuit points out that candidates for statewide office only need 5,000 signatures, in partisan primaries.  The analogy between a partisan primary and a non-partisan election is not perfect, but it is close.  In Chicago city office elections, if no one gets at least 50% of the vote in the first round, a run-off is held.

In 1979 the U.S. Supreme Court ruled that it was unconstitutional to require minor party and independent candidates for Mayor of Chicago to obtain approximately 42,000 signatures, because minor party and independent candidates for statewide partisan office needed 25,000 signatures.  The Court basically said that it is not rational to require more signatures for an office in just part of the state, than for statewide office.  The decision was unanimous.  The U.S. Supreme Court repeated that in 1992 in Norman v Reed.

Chicago switched to non-partisan elections for its citywide city offices in 1999.  Thanks to Christina Tobin for this news.