All persons in whom any right to relief arising out of any order, determination, rule or regulation is alleged to exist, whether jointly or severally, may join in one proceeding as petitioners, where, if such persons brought separate petitions, any common question of law or fact would arise; provided that, if it appears to the Board that joinder may embarrass, delay or prejudice a substantial right or the disposition of the matter, the Board may sever the proceeding and order separate hearings or any other order as may be expedient.
N.Y. Comp. Codes R. & Regs. Tit. 12 § 65.66