New York Codes, Rules and Regulations
Title 20 - DEPARTMENT OF TAXATION AND FINANCE
Chapter II - Income Taxes and Estate Taxes
Subchapter E - New York City Personal Income Tax On Residents
Part 293 - Joint Collection And Enforcement Activity
Section 293.1 - Joint assessment of taxes and proportionate division of payment

Tax Law, § 1311(a); Administrative Code of the City of New York, § 11-1799(a)-(b)

If there is assessed a tax imposed pursuant to chapter 17 of title 11 of the Administrative Code of the City of New York, and there is also assessed a tax or taxes against the same taxpayer pursuant to article 22 of the Tax Law, article 23 of the Tax Law (for years such article was in effect), chapter 19 of title 11 of the Administrative Code of the City of New York, or article IX or X of the Codes and Ordinances of the City of Yonkers, and payment of a single amount is required under the provisions of section 292.2 of this Title, such payment shall be deemed to have been made with respect to the taxes so assessed in proportion to the amount of such taxes due, including tax, penalties, interest and additions to tax. For the rate of interest on overpayments, underpayments and recovery of erroneous refunds, see Part 2393 of this Title.