N.Y. Second Class Cities Law § 72
Unless under special laws governing the city at the time this chapter takes effect provision is made for the creation or maintenance of a sinking fund or funds for any purpose, thirty per centum of all moneys or revenues received by any city which has term bonds outstanding and unpaid, or by any officer, board or department thereof, from any source other than taxes or loans shall, upon receipt of the same, be forthwith deposited in a separate account or accounts in one or more of the designated fiscal depositories of the city to the credit of the bonded indebtedness of the city, and said deposit shall be known as the sinking fund. The sinking fund shall be used exclusively for the payment, as it matures, of the principal of the indebtedness of the city evidenced by term bonds other than bonds issued for improvements financed by assessments for benefit or bonds issued prior to the effective date of the local finance law, in anticipation of the collection of revenues. If, under the special laws governing the city at the time this chapter takes effect, provision is made for the creation or maintenance of a sinking fund or funds for any purpose, such sinking fund or funds shall continue and be maintained as provided in such laws.
N.Y. Second Class Cities Law § 72