NY Tax Law §651(b)(4) (b) Husband and wife.

(4) If either husband or wife is a resident and the other is a nonresident or part-year resident, they shall file separate New York income tax returns, in which event their tax liabilities shall be separate, unless such husband and wife determine their federal taxable income jointly and both elect to determine their joint New York taxable income as if both were residents, in which event their tax liabilities shall be joint and several except as provided in paragraph six of this subsection, section six hundred fifty-four and subsection (e) of section six hundred eighty-five.