N.Y. Real Prop. Acts. Law § 734
In the county of Westchester, if the local legislative body has, by local law, opted to require such notice, service of a copy of the notice of petition and petition in any proceeding commenced against a residential tenant in accordance with the provisions of this article shall be served upon the county commissioner of social services. Such service shall be made by certified mail, return receipt requested, directed to an address set forth in the local law, or pursuant to the provisions of the civil practice law and rules. Such service shall be made at least five days before the return date set in the notice of petition. Proof of such service shall be filed with the court. Failure to serve the commissioner shall not be a jurisdictional defect, and shall not be a defense to a proceeding brought pursuant to the provisions of this article.
N.Y. Real Prop. Acts. Law § 734