N.Y. Comp. Codes R. & Regs. tit. 20, § 111.2 – New York taxable income of husband and wife.

(a) Where both a husband and wife are residents and they determine their Federal taxable incomes separately on separate Federal income tax returns, they must also determine their New York taxable incomes separately on separate New York State personal income tax returns (also see section 651[b][1] of the Tax Law).
(b) Where both a husband and wife are residents and they determine their Federal taxable income on a joint Federal income tax return, they must also determine their New York taxable income jointly on a joint New York State personal income tax return (also see section 651[b][2] of the Tax Law).
(c) If neither husband or wife, both of whom are residents, files a Federal income tax return, they may determine their New York taxable income jointly on a joint New York State personal income tax return, or if both so elect, they may determine their New York taxable incomes separately on separate New York State personal income tax returns (also see section 651[b][3] of the Tax Law).
1. (1) If either the husband or the wife is a resident of New York State for the entire taxable year and the other is a nonresident or part- year resident during such taxable year, they must each determine their New York taxable income on separate New York State personal income tax returns unless they:
  1. (i) file a joint Federal income tax return; and
  2. (ii) they elect to file a joint New York State personal income tax return determining their joint New York taxable income as if both the husband and wife were residents of New York State for the entire taxable year (also see section 651[b] [4] of the Tax Law).
2. (2) The election described in paragraph (1) of this subdivision applies only in those cases where one spouse was a resident of New York State for the entire taxable year and the other spouse was a nonresident or part-year resident during such taxable year. Such election does not apply in cases where both the husband and the wife changed their residence (either at the same time or at different times) during the taxable year or where one spouse is a nonresident of New York State for the entire taxable year and the other spouse is a part-year resident. Section 651(b)(1), (2) or (3) of the Tax Law is applicable in determining the filing requirements in such situations.
(d) Husband and wife with different resident status.

Tax Law, § 611(b)