N.Y. CVP Law § 3019

§ 3019. Counterclaims and cross-claims. (a) Subject of counterclaims.\nA counterclaim may be any cause of action in favor of one or more\ndefendants or a person whom a defendant represents against one or more\nplaintiffs, a person whom a plaintiff represents or a plaintiff and\nother persons alleged to be liable.\n (b) Subject of cross-claims. A cross-claim may be any cause of action\nin favor of one or more defendants or a person whom a defendant\nrepresents against one or more defendants, a person whom a defendant\nrepresents or a defendant and other persons alleged to be liable. A\ncross-claim may include a claim that the party against whom it is\nasserted is or may be liable to the cross-claimant for all or part of a\nclaim asserted in the action against the cross-claimant.\n (c) Counterclaim against trustee or nominal plaintiff. In an action\nbrought by a trustee or in the name of a plaintiff who has no actual\ninterest in the contract upon which it is founded, a claim against the\nplaintiff shall not be allowed as a counterclaim, but a claim existing\nagainst the person beneficially interested shall be allowed as a\ncounterclaim to the extent of the plaintiff's claim, if it might have\nbeen so allowed in an action brought by the person beneficially\ninterested.\n (d) Cause of action in counterclaim or cross-claim deemed in\ncomplaint. A cause of action contained in a counterclaim or a\ncross-claim shall be treated, as far as practicable, as if it were\ncontained in a complaint, except that separate process, trial or\njudgment may not be had unless the court so orders. Where a person not a\nparty is alleged to be liable a summons and answer containing the\ncounterclaim or cross-claim shall be filed, whereupon he or she shall\nbecome a defendant. Service upon such a defendant shall be by serving a\nsummons and answer containing the counterclaim or cross-claim. Such\ndefendant shall serve a reply or answer as if he or she were originally\na party.\n