105 ILCS 5/17-11.1
When a school board has authority to levy taxes at the maximum permissive tax rate allowed by law or the maximum tax rate allowed by voter approved referendum and, after the certificate of tax levy has been filed, a change in the assessed valuation resulting from the application of the equalization multiplier by the Department of Revenue causes the school district's tax extensions to be less than the maximum permissive tax rate allowed by law or the maximum tax rate allowed by voter approved referendum, the school board may, within 20 days of such change, amend the certificate of tax levy to provide for the maximum amount of tax extensions provided by the permissive tax rate or by the voter approved referendum, as limited by the Property Tax Extension Limitation Law.
105 ILCS 5/17-11.1