N.Y. Second Class Cities Law § 79
No officer, board, or department shall, during any fiscal year, expend or contract to be expended any money or incur any liability, or enter into any contract which, by its terms, involves the expenditure of money for any of the purposes for which provision is made in the annual estimate in excess of the amounts appropriated in said estimate, as adopted by the common council, for such officer, board, department or purpose, for such fiscal year. Any contract, verbal or written, made in violation of this section shall be null and void as to the city, and no moneys belonging to the city shall be paid thereon, provided, however, that nothing herein contained shall prevent the making of contracts for light or water, the collection and disposal or the disposal of garbage, the collection and removal of rubbish and ashes, the cleaning of streets, or the sprinkling of streets or public places by railway cars, for periods exceeding one year.
Nothing herein contained, however, shall be held to prohibit the expenditure of such sums as may be made available, pursuant to section seventy-six of this chapter or section 29.00 of the local finance law.
N.Y. Second Class Cities Law § 79