2015 New York Laws
CVP - Civil Practice Law & Rules
Article 10 - (Civil Practice Law & Rules) PARTIES GENERALLY
1003 - Nonjoinder and misjoinder of parties.

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