Rule 20(a)(2) permits joinder of a number of defendants in one cause of action if (A) any right to relief is asserted against them jointly, severally, or in the alternative with respect to or arising out of the same transaction, occurrence, or series of transactions or occurrences; and (B) any question of law or fact common to all defendants will arise in the action. Fed.R.Civ.P. 20(a)(2).
Rule 20 is permissive. Compare Fed.R.Civ.P. 20(a)(2) (stating that '[p]ersons . . . may be joined in one action as defendants') (emphasis added), with Fed.R.Civ.P. 19 (addressing required joinder of parties). The purpose of the rule is 'to promote trial convenience and expedite the final determination of disputes, thereby preventing multiple lawsuits.' 7 Charles Alan Wright, Arthur R. Miller & Mary Kay Kane, Federal Practice and Procedure § 1652, at 395 (3d ed. 2001) (Wright, Miller & Kane). The Court's discretion, however, is not unlimited. To be joined, the right to relief must relate to or arise out of the same transaction or occurrence. Id. § 1653.
'The transaction and common-question requirements prescribed by Rule 20(a) are not rigid tests. They are flexible concepts used by the courts to implement ...