Tax Law, § 5(b) of § 1340(c); Codes and Ordinances of the City of Yonkers, § 92-102(b)
A nonresident taxpayer may not change his taxable year unless a similar change has been made for Federal income tax purposes, except where a change is authorized by the State Tax Commission with respect to a taxpayer not required to file a Federal income tax return. If a taxpayer's taxable year is changed for Federal income tax purposes, such taxpayer's taxable year for purposes of the City of Yonkers earnings tax must be similarly changed.
N.Y. Comp. Codes R. & Regs. Tit. 20 § 261.2