N.J. Ct. R. 4:33
Rule 4:33-1. Intervention as of Right
Upon timely application anyone shall be permitted to intervene in an action if the applicant claims an interest relating to the property or transaction which is the subject of the action and is so situated that the disposition of the action may as a practical matter impair or impede the ability to protect that interest, unless the applicant's interest is adequately represented by existing parties.
Rule 4:33-2. Permissive Intervention
Upon timely application anyone may be permitted to intervene in an action if the claim or defense and the main action have a question of law or fact in common. When a party to an action relies for ground of claim or defense upon any statute or executive order administered by a state or federal governmental agency or officer, or upon any regulation, order, requirement or agreement issued or made pursuant to the statute or executive order, the agency or officer upon timely application may be permitted to intervene in the action. In exercising its discretion the court shall consider whether the intervention will unduly delay or prejudice the adjudication of the rights of the original parties.
Rule 4:33-3. Procedure
A person desiring to intervene shall file and serve on all parties a motion to intervene stating the grounds therefor and accompanied by a pleading setting forth the claim or defense for which intervention is sought along with a Case Information Statement pursuant to R. 4:5-1(b)(1). The appropriate filing fee for the proposed pleading shall be paid at the time of filing the motion to intervene but shall be returned if that motion is denied.
N.J. Ct. R. 4:33