70 ILCS 2605/11.15

No person shall be employed upon contracts for work to be done by any such sanitary district unless he or she is a citizen of the United States, a national of the United States under Section 1401 of Title 8 of the United States Code, a person lawfully admitted for permanent residence under Section 1101 of Title 8 of the United States Code, an individual who has been granted asylum under Section 1158 of Title 8 of the United States Code, or an individual who is otherwise legally authorized to work in the United States.