N.Y. CVP. LAW § 901 : NY Code - Section 901: Prerequisites to a class action

a. One or more members of a
  class may sue or be sued as representative parties on behalf of all if:
    1. the class is so numerous  that  joinder  of  all  members,  whether
  otherwise required or permitted, is impracticable;
    2.  there  are  questions  of  law  or  fact common to the class which
  predominate over any questions affecting only individual members;
    3. the claims or defenses of the representative parties are typical of
  the claims or defenses of the class;
    4. the representative parties will fairly and adequately  protect  the
  interests of the class; and
    5.  a class action is superior to other available methods for the fair
  and efficient adjudication of the controversy.
    b. Unless a statute creating or  imposing  a  penalty,  or  a  minimum
  measure  of  recovery  specifically authorizes the recovery thereof in a
  class action, an action to recover a  penalty,  or  minimum  measure  of
  recovery  created or imposed by statute may not be maintained as a class