From the IBA:
On 6/5/13 the Chicago City Council passed a Tenants Rights Ordinance which imposes mandatory relocation fees and rent control requirements on mortgagees and judicial sale purchasers when the property includes residential rentals. The ordinance is expected to be published 6/26/13, making the effective date 9/24/13.

See here: https://www.ilbanker.com/Documents/GR/Chicago_Renting_Sub_May302013.pdf

My favorite part is that you have to give them the notice in English, Spanish, Chinese and Polish. The ghost of Casimir Pulaski strikes again!