Haw. R. Civ. P. 24

(a) Intervention of right. Upon timely application anyone shall be permitted to intervene in an action: (1) when a statute confers an unconditional right to intervene; or (2) when the applicant claims an interest relating to the property or transaction which is the subject of the action and the applicant is so situated that the disposition of the action may as a practical matter impair or impede the applicant's ability to protect that interest, unless the applicant's interest is adequately represented by existing parties.

(b) Permissive intervention. Upon timely application anyone may be permitted to intervene in an action: (1) when a statute confers a conditional right to intervene; or (2) when an applicant's 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, ordinance or executive order administered by an officer, agency or governmental organization of the State or a county, or upon any regulation, order, requirement or agreement issued or made pursuant to the statute, ordinance or executive order, the officer, agency or governmental organization 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.

(c) Procedure. A person desiring to intervene shall serve a motion to intervene upon the parties as provided in Rule 5. The motion shall state the grounds therefor and shall be accompanied by a pleading setting forth the claim or defense for which intervention is sought. The same procedure shall be followed when a statute gives a right to intervene.

(d) Notice of Claim of Unconstitutionality. A party who draws into question the constitutionality of a Hawaiʻi statute, in any proceeding to which the State of Hawaiʻi, or any agency thereof, or any officer or employee thereof in an official capacity is not a party, shall provide immediate written notice of the constitutional issue to the Attorney General of the State of Hawaiʻi.

(Amended May 15, 1972, effective July 1, 1972; further amended December 7, 1999, effective January 1, 2000; further amended April 17, 2006, effective July 1, 2006.)