Tax Law, § 659

A taxpayer who files an amended Federal income tax return or an employer who files an amended Federal return of income tax withheld must also file, within 90 days thereafter, a similarly amended New York State income tax return(s) with the Tax Commission and must pay the additional New York State income tax, if any, shown to be due thereon. The amended New York State income tax return to be filed with respect to an employer filing an amended Federal return of income tax withheld must be filed on form IT-2101 (PNS) marked “amended” and must be accompanied by a statement showing the amount of New York State personal income tax originally withheld and reported, the amount of New York State personal income tax which should have been withheld and reported, and the reason for the increase in the amount on New York State personal income tax required to be withheld and reported.