N.J. Ct. R. 4:29-1

(a) Joinder by Parties. All persons may join in one action as plaintiffs or be joined as defendants jointly, severally, in the alternative, or otherwise, if the right to relief asserted by the plaintiffs or against the defendants arises out of or in respect of the same transaction, occurrence, or series of transactions or occurrences and involves any question of law or fact common to all of them. A plaintiff or defendant need not be interested in obtaining or defending against all the relief demanded. Judgment may be given for one or more of the plaintiffs according to their respective rights to relief, and against one or more defendants according to their respective liabilities.

(b) Joinder by Order of the Court. The court on its own motion may order the joinder of any person subject to service of process whose existence was disclosed by the notice required by R. 4:5-1(b)(2) or by any other means who may be liable to any party on the basis of the same transactional facts. The court shall not order such joinder unless it finds for specific reasons stated on the record that the interests of judicial economy and of non-parties which would be served by such joinder substantially outweigh the interests of the named parties in not joining additional parties.

(c) Certain Tax Foreclosure and Condemnation Actions. Anything in paragraph (a) of this rule to the contrary notwithstanding:

(1) A purchaser of a tax sale certificate (other than a municipality) or the purchaser's heirs or assigns may file a complaint to foreclose the right of redemption and may join therein 2 or more separate causes of action, or causes of action founded upon 2 or more certificates of sale of the same municipality and of the same or different tracts of land, covering but not exceeding 15 tax sale certificates.

(2) Where a municipality has acquired lands by purchase at sales held to enforce a tax or other municipal lien, it may join in an action to foreclose the right of redemption of such lands, causes of action to foreclose such rights of redemption, covering but not exceeding 15 tax sale certificates.

(3) The plaintiff in an action under N.J.S.A. 54:5-104.29 et seq. (In Rem Tax Foreclosure Act) may join in the action not more than 200 tax sale certificates.

(4) The plaintiff in an action under R.S. 54:8-3 (Destruction or Loss of Public Tax Records) may join in the action any number of separate parcels of land of the same owner.

(5) The plaintiff in an action for condemnation may join in the action not more than 10 separate parcels of land, except by leave of court.

(6) The plaintiff in an action for foreclosure of timeshare mortgages may join in the action not more than 10 separate timeshare units, provided all involve the same timeshare plan and the nature of the default is substantially the same for each timeshare mortgage joined.

(7) The court may order any action to which this rule applies severed and the provisions of R. 4:4-4 and R. 4:4-5 for service with process of a copy of the complaint upon all defendants may not be relaxed.