N.Y. Comp. Codes R. & Regs. tit. 20 § 261.1
Tax Law, § 5(a) of § 1340(c); Codes and Ordinances of the City of Yonkers, § 92-102(a)
The taxable year of a nonresident taxpayer required to make a City of Yonkers earnings tax return, under article 30-B of the Tax Law and article X of the Codes and Ordinances of the City of Yonkers, must be the same as such nonresident taxpayer's taxable year for Federal income tax purposes. Similarly, the taxable year of a partnership required to make a City of Yonkers partnership return (see section 267.9 of this Title) must be the same as the partnership's taxable year for Federal income tax purposes. The taxable year may be a calendar year or a fiscal year consisting of 12 months. However, under certain circumstances, the period may be less than 12 months (e.g., in case of death, change of accounting period or change of resident status), or it may be a 52-53 week year.
A nonresident taxpayer who is not required to file a Federal income tax return, but who is required to file a City of Yonkers earnings tax return, must report on the calendar year basis unless the State Tax Commission authorizes the use of a different taxable period. This rule does not apply, however, in a case where a taxpayer had for a previous year filed a Federal income tax return and such taxpayer's taxable year for Federal income tax purposes for the last such year, in respect of which a Federal income tax return was filed, was other than the calendar year. Thus, if the last Federal income tax return filed by a taxpayer was on the basis of a fiscal year ending June 30th, and such taxpayer is not required to file a Federal income tax return for the subsequent taxable year but is required to file a City of Yonkers earnings tax return, such taxpayer's taxable period for the City of Yonkers earnings tax purposes for such year and thereafter is a fiscal year ending June 30th. If a taxpayer not required to file a Federal income tax return is subsequently required to file a Federal income tax return and the taxable period for Federal purposes is different from the taxable period established for City of Yonkers earnings tax purposes, his City of Yonkers taxable period will be changed to conform to the Federal taxable period.
N.Y. Comp. Codes R. & Regs. Tit. 20 § 261.1