New York Codes, Rules and Regulations
Title 20 - DEPARTMENT OF TAXATION AND FINANCE
Chapter II - Income Taxes and Estate Taxes
Subchapter D - City Of Yonkers Earnings Tax On Nonresidents
Part 263 - Who Must File A City Of Yonkers Earnings Tax Return
Section 263.5 - City of Yonkers returns in case of a change of residence

Tax Law, § 1327, § 12 of § 1340(c); Codes and Ordinances of the City of Yonkers, §§ 92-86, 92-109

A taxpayer who changes residence to or from the City of Yonkers during the tax year may be required to file two returns-a City of Yonkers income tax surcharge return for the period of residence and a City of Yonkers earnings tax return for the period of nonresidence if there are wages or net earnings from self-employment subject to the City of Yonkers earnings tax on nonresidents during the period of nonresidence (see Parts 253 and 266 of this Title).