225 ILCS 64/20

In addition to any other information required to be contained in an application for licensure under this Act, every application for an original license under this Act shall include the applicant's social security number, which shall be retained in the agency's records pertaining to the license. For applicants without a social security number, an individual taxpayer identification number shall be provided instead of a social security number. As soon as practical, the Department shall assign a customer's identification number to each applicant for a license. Every application for a renewal or restored license shall require the applicant's customer identification number.