The Illinois Human Rights Act prohibits employers from discriminating on the basis of race, color, religion, national origin, ancestry, age (40 years and over), sex, marital status, order of protection status, disability, military status, sexual orientation, unfavorable discharge from military service (except dishonorable discharge), or citizenship status, unless the characteristic is a bona fide occupational qualification (BFOQ) (IL Comp. Stat. Ch. 775 Sec. 5/1-101, Sec. 5/2-104). Therefore, application forms should not inquire about any of these characteristics. The Act covers employers with 15 or more employees, except for the prohibitions of sexual harassment and disability discrimination, which apply to all employers, regardless of size (IL Comp. Stat. Ch. 775 Sec. 5/2-101).
Retaliation prohibited. It is also unlawful to retaliate against any individual who opposes any of the preceding discriminatory practices or because he or she has made a charge, filed a complaint, testified, assisted, or participated in an investigation, proceeding, or hearing under the Act (IL Comp. Stat. Ch. 775 Sec. 5/6-101). "Retaliation" includes the refusal to hire a person who filed a discrimination charge against another employer (Carter Coal Co. v. Human Rights Cmsn., 261 Ill. App. 3d 1 (1994)).
There is additional information available regarding discrimination based on citizenship status.