N.Y. Comp. Codes R. & Regs. tit. 20, § 263.6
If a nonresident taxpayer has a short taxable period due to a change in accounting period, such nonresident taxpayer must file a City of Yonkers earnings tax return if such taxpayer has any wages earned, or net earnings from self-employment derived from, within the City of Yonkers during such short taxable period.