30 ILCS 425/14
The State of Illinois irrevocably covenants and agrees with the holders of Bonds issued pursuant to this Act that the State will not limit or alter (a) the basis on which the taxes and revenues of the State are required to be collected and deposited in the Build Illinois Fund created under "An Act in relation to State finance", approved June 10, 1919, as amended, pursuant to Section 6z-9 of that Act and to be credited to and transferred from the Build Illinois Bond Account pursuant to Section 8.25 of that Act; (b) the basis on which transfers of amounts credited to the Build Illinois Bond Account are required to be made to the Build Illinois Bond Retirement and Interest Fund; (c) the purposes of the Build Illinois Bond Retirement and Interest Fund; or (d) the provisions of this Section 14, or of Sections 11, 12 and 13 of this Act or the provisions of Sections 6z-9 or 8.25 of "An Act in relation to State finance", approved June 10, 1919, as amended, so as to impair, in any of the foregoing respects, the obligations of contract incurred by the State in favor of the holders of Bonds issued under this Act. The covenant and agreement set forth in this Section may be included in any Bond Sale Order, trust indenture, agreement or Bond authorized under this Act.
30 ILCS 425/14