N.Y. Tax Law § 1439-B
Notwithstanding any other provisions of law to the contrary, the county of Columbia, acting through its local legislative body, is hereby authorized and empowered to adopt and amend local laws imposing in such county a tax on each conveyance of real property or interest therein when the consideration exceeds five hundred dollars, at the rate of one dollar for each five hundred dollars or fractional part thereof, provided, however, that the first one hundred fifty thousand dollars of any single family residence shall be exempt from such tax. Such local law shall apply to any conveyance occurring on or after the first day of a month to be designated by such legislative body, which is not less than sixty days after the enactment of such local laws, but shall not apply to conveyances made on or after such date pursuant to binding written contracts entered into prior to such date, provided that the date of execution of such contract is confirmed by independent evidence such as the recording of the contract, payment of a deposit or other facts and circumstances as determined by the treasurer.
N.Y. Tax Law § 1439-B