20 ILCS 2505/2505-275
In the case of overpayment of any tax liability arising from an Act administered by the Department, the Department may credit the amount of the overpayment and any interest thereon against any final tax liability arising under that or any other Act administered by the Department. The Department may enter into agreements with the Secretary of the Treasury of the United States (or his or her delegate) to offset all or part of an overpayment of such a tax liability against any liability arising from a tax imposed under Title 26 of the United States Code. The Department may collect a fee from the Secretary of the Treasury of the United States (or his or her delegate) to cover the full cost of offsets taken, to the extent allowed by federal law, or, if not allowed by federal law, from the taxpayer by offset of the overpayment.
20 ILCS 2505/2505-275