N.Y. CVP Law § 1003

§ 1003. Nonjoinder and misjoinder of parties. Nonjoinder of a party\nwho should be joined under section 1001 is a ground for dismissal of an\naction without prejudice unless the court allows the action to proceed\nwithout that party under the provisions of that section. Misjoinder of\nparties is not a ground for dismissal of an action. Parties may be added\nat any stage of the action by leave of court or by stipulation of all\nparties who have appeared, or once without leave of court within twenty\ndays after service of the original summons or at anytime before the\nperiod for responding to that summons expires or within twenty days\nafter service of a pleading responding to it. Parties may be dropped by\nthe court, on motion of any party or on its own initiative, at any stage\nof the action and upon such terms as may be just. The court may order\nany claim against a party severed and proceeded with separately.\n