N.Y. Real Prop. Tax Law § 581-A
Notwithstanding any other provision of law, the assessed valuation of real property used for residential rental purposes where at least twenty percent of the residential units are subject to an agreement with a municipality, the state, the federal government, or an instrumentality thereof, which agreement restricts occupancy of those units to tenants who qualify in accordance with an income test, shall be determined using the income approach as applied to the actual net operating income, after deducting for reserves required by any federal, state or municipal programs. For the purposes of this section "net operating income" shall mean the actual or anticipated net income that remains after all operating expenses are deducted from effective gross income, but before mortgage debt service and book depreciation are deducted. The assessed valuation of real property used for such residential rental purposes shall be determined using the actual net operating income, and shall not include federal, state or municipal income tax credits, subsidized mortgage financing, or project grants, where such subsidies are used to offset the project development cost in order to provide for lower initial rents as determined by regulations promulgated by the division of housing and community renewal.
N.Y. Real Prop. Tax. Law § 581-A