65 ILCS 20/21-40
If the city council shall fail at any time to pass a redistricting ordinance as required in this article, one-fifth or more of the alderpersons elected shall have the right to file with the city clerk, not less than 40 days before the date of holding any general, municipal, or special election, to be held in and for the entire city, an ordinance redistricting the city in accordance with the provisions of this article, together with a petition signed by them demanding that such ordinance be submitted to the legal voters at the next such election in and for the entire city to be held not less than 40 days after the filing of such ordinance and petition: Provided, that no alderperson shall have the right to sign more than one such petition. Upon the expiration of the time for filing any such ordinance the city clerk shall promptly certify to the board of election commissioners of the city of Chicago any ordinance or ordinances, together with any petition or petitions, so filed and thereupon it shall be the duty of the board of election commissioners to submit such ordinance or ordinances to a popular vote at the election specified in such petition or petitions: Provided, that if, after the filing of any such ordinance and petition and not less than 40 days prior to such election, the city council shall pass an ordinance redistricting the city, then the question of the adoption of any ordinance or ordinances filed with the city clerk in accordance with the provisions of this section shall not be submitted to a popular vote. However, after such action by the city council, a substitute ordinance or ordinances may be proposed in the manner provided in this article.
65 ILCS 20/21-40