New York Consolidated Laws, Real Property Law - RPP § 389. Any person interested may appear and defend

Any person interested in the property, or whose interests may be affected by the final order or judgment of registration in the proceeding, whether specifically named in the notice or not, may enter his appearance by serving a copy of the same on the registrar of the county in which the property is located and with the clerk of the supreme court in such county, and filing the original thereof together with proof of service with the county clerk on or before the return day or within such further time as may be allowed by the court;  and may enter his objections, if any, by likewise serving a copy of the same on the registrar of the county in which the property is located and with the clerk of the supreme court in such county, and filing the original thereof together with proof of service with the county clerk on or before the return day or within such further time as may be allowed by the court;  and may oppose the petition for registration of the property as belonging to the petitioner, or set up a cross-demand to have the title registered in his own behalf.  In any case, he shall state particularly what his interest is and shall specifically state all objections to the petition.