35 ILCS 5/702
For purposes of this Section an employee shall be entitled to a withholding exemption in an amount equal to the basic amount in Section 204(b) for each personal or dependent exemption which he is entitled to claim on his federal return pursuant to Section 151 of the Internal Revenue Code ; plus an allowance equal to 1,000 for each 1,000 he is entitled to deduct from gross income in arriving at adjusted gross income pursuant to Section 62 of the Internal Revenue Code ; plus an additional allowance equal to 1,000 for each 1,000 eligible for subtraction on his Illinois income tax return as Illinois real estate taxes paid during the taxable year; or in any lesser amount claimed by him. Every employee shall furnish to his employer such information as is required for the employer to make an accurate withholding under this Act. The employer may rely on this information for withholding purposes. If any employee fails or refuses to furnish such information, the employer shall withhold the full rate of tax from the employee's total compensation.
35 ILCS 5/702