New York Consolidated Laws, General City Law - GCT § 11. City taxable income of a resident individual

(b) Husband and wife.  (1) If the federal taxable income of husband or wife is determined on a separate federal return, their city taxable incomes shall be separately determined.

(2) If the federal taxable income of husband and wife is determined on a joint federal return, or if neither files a federal return:

(3) If either husband or wife is a resident and the other is a nonresident, the tax of the resident shall be determined on his separate city taxable income, unless both elect to determine their joint city taxable income as if both were residents.