Rule 24.Intervention.

Rule 24 gives two paths into someone else's lawsuit. Intervention of right applies when a statute grants an unconditional right to join, or when the applicant has an interest in the property or transaction at stake and a decision in the case could, as a practical matter, impair the applicant's ability to protect that interest, unless the existing parties already protect it adequately. Permissive intervention is up to the court's discretion, available when a statute grants a conditional right to intervene, or when the applicant's claim or defense shares a question of law or fact with the main action; a government agency may also intervene when a party's claim or defense rests on a statute, ordinance, or regulation the agency administers. Either way, the court weighs whether letting the newcomer in will unduly delay or prejudice the original parties.

To intervene, a person serves a motion on the existing parties the same way any paper is served under Rule 5, stating the grounds for intervention and attaching a pleading that sets out the claim or defense being asserted. The same procedure applies when a statute independently gives someone a right to intervene. Separately, Rule 24(d) requires a party who challenges the constitutionality of a Hawai'i statute, in a case where the State isn't already a party, to give the Attorney General immediate written notice of the constitutional question.