N.Y. Real Property Actions & Proceedings Law § 1511

§ 1511. Additional parties. 1. In an action brought under this\narticle, the person in possession shall be made a party to the action,\nand when such person claims the right of possession, or an interest in\nthe real property, under another, such other person shall also be made a\nparty.\n 2. Where it appears to the court that a person not a party to the\naction may have an estate or interest in the real property which may in\nany manner be affected by the judgment, the court, upon application of\nsuch person, or of any party to the action, or on its own motion, may\ndirect that such person be made a party.\n