105 ILCS 5/34-48
After the effectiveness of the budget (other than an interim budget), the board shall not make any other appropriations prior to the adoption or passage of the next succeeding budget. The board may not, either directly or indirectly, make any contract or do any act which shall add to its expenditures or liabilities, in any fiscal year, any thing or sum above the amount provided for in the budget for that fiscal year except that the board may, at any time after the adoption of the annual school budget, by a 2/3 vote of the full membership of the board, pass an additional or supplemental budget, thereby adding appropriations to those made in the annual school budget and such supplemental or additional school budget shall be regarded as an amendment of the annual school budget for that year; provided that any such additional or supplemental appropriations so made shall not exceed the amount of additional moneys which the board of education will have available for appropriation in that year from any source, including any fund balances not previously appropriated, over and above the amount of moneys which the board, at the time of the adoption of its annual budget for that year, estimated would be available for appropriation from such sources, or provided that the board, by a concurring vote of 2/3 of all the members thereof (said votes to be taken by yeas and nays and entered in the proceedings of the board) may make any expenditures and incur any liability rendered necessary to meet emergencies such as epidemics, fires, unforeseen damages or other catastrophes happening after the annual school budget has been passed or adopted. This section does not prevent the board from providing for and causing to be paid from its funds any charge imposed by law without the action of the board.
105 ILCS 5/34-48