During any fiscal year the City Council may adopt a supplemental appropriation ordinance in an amount not in excess of the aggregate of any additional revenue available to the city, or estimated to be received by the city subsequent to the adoption of the annual appropriation ordinance for the fiscal year. Such supplemental appropriation ordinance shall only affect revenue that was not available for appropriation when the annual appropriations ordinance was adopted.
(ILCS Ch. 65, Act 5 § 8-2-7) (‘69 Code, § 2-7)