Generally, the employer may not deduct from your paycheck unless you have previously agreed to the deduction in writing. You can file a claim with the Illinois Department of Labor and/or speak to an experienced employment attorney. Many of us, myself included, will provide a free consultation.
This answer is provided for informational purposes only and should not be relied on as legal advice. You should be aware that no attorney-client relationship is established through this answer and none will be established without a personal consultation and the signing of an engagement agreement.