(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.
Rule 24.Intervention
Last amended November 1, 2023 · Last verified July 8, 2026
In one sentenceRule 24 lets a nonparty join a pending lawsuit either as a matter of right, when a statute grants that right or the case threatens an unprotected interest of theirs, or with the court's permission, when their claim or defense shares a common question with the case, and separately guarantees the State of Maine a chance to intervene whenever a statute's constitutionality is challenged in a suit the State is not already part of.
Full Text of Rule 24
(b) Permissive Intervention. Upon timely application anyone may be permitted to intervene in an action 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 or executive order administered by a federal or state governmental officer or agency or upon any regulation, order, requirement, or agreement issued or made pursuant to the statute or executive order, the officer or agency 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 or, if the motion is filed through electronic filing as defined in Rule 2 of the Maine Rules of Electronic Court Systems, as provided in Rule 36 of the of the Maine Rules of Electronic Court Systems. 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.
(d) Intervention by the State. When the constitutionality of an act of the legislature affecting the public interest is drawn in question in any action to which the State of Maine or an officer, agency, or employee thereof is not a party, the plaintiff shall notify the Attorney General, and the court shall permit the State of Maine to intervene for presentation of evidence, if evidence is otherwise admissible in the case, and for argument on the question of constitutionality.
Advisory Committee’s Notes & Reporter’s Notes
Advisory Note – November 2023
Rule 24(c) is amended to include references to the Maine Rules of Electronic Court Systems.
Advisory Committee’s Notes — May 1, 2000
Subdivision (d) is changed to put the burden on a plaintiff, rather than the court to notify the Attorney General when constitutionality of a law is challenged.
Explanation of Amendments — November 1, 1966
The amendment to Rule 24(a) was taken from a 1966 amendment to F.R. 24(a). M.R.C.P. 24(a) departed substantially from the original F.R. 24(a) and was intended to preserve the existing Maine law on intervention. The 1966 federal amendment eliminated the difficulties in the federal rule which led to this departure, and Maine has now followed the federal model in its amended form. Instead of making the test for intervention of right whether the would-be intervenor “will either gain or lose by the direct legal effect of the judgment,” the amended rule resorts to the pragmatic consideration of whether the disposition of the action may as a practical matter impair or impede the applicant’s ability to protect his interests. This approach draws upon the 1966 revision of Rule 19 and the reasoning underlying it.
The amendment also specifically provides, as M.R.C.P. 24(a) did not, that intervention is not allowed if the applicant’s interest is adequately represented by existing parties.
The purpose of the amendment to Rule 24(c) was to eliminate an inconsistency with Rule 5(a).
Reporter’s Notes — December 1, 1959
This rule is derived from Federal Rule 24 but changes have been made in Rule 24(a)* and the substance of Federal Rule 24(c) has been split between Rule 24(c) and a new Rule 24(d). The reason for the separation is to give emphasis to the right of the State of Maine to intervene when the constitutionality of a statute is questioned in a case to which the State is not a party. This is new to Maine law except in limited circumstances. See R.S.1954, Chap. 107, Sec. 48 [now 14 M.R.S.A. § 5963].
Intervention is a familiar equity procedure. Whitehouse, Equity Practice §§ 319-320. The rule is somewhat broader than the general practice as to permissive intervention and is somewhat simpler procedurally.
* [Field, McKusick & Wroth commented: “1966 amendments to both the Maine and federal rules have brought them into substantial uniformity.” 1 Field, McKusick & Wroth, Maine Civil Practice at 399 (2d ed. 1970).]
Plain-English Summary
Intervention lets someone outside a lawsuit step into it because the outcome will affect them directly. Subdivision (a) grants intervention as of right in two situations: when a statute confers an unconditional right to intervene, or when the applicant has an interest in the property or transaction at issue that a judgment might practically impair, and no existing party adequately represents that interest. Subdivision (b) covers permissive intervention — the court has discretion to let someone in whose claim or defense shares a common question of law or fact with the main action, including a government officer or agency relying on a statute, order, or regulation at issue in the case, weighing whether intervention would unduly delay or prejudice the original parties.
Subdivision (c) sets the mechanics: a motion to intervene, served like any other motion, accompanied by a pleading laying out the claim or defense for which intervention is sought. Subdivision (d) addresses a distinct public interest: whenever a Maine statute’s constitutionality is challenged in a case the State is not already part of, the plaintiff must notify the Attorney General, and the court must let the State intervene to present evidence and argument on the constitutional question.
Frequently Asked Questions
What is the difference between intervention of right and permissive intervention?
Intervention of right, under subdivision (a), must be granted when a statute confers that right or when the applicant's interest in the case could be practically impaired and no existing party adequately represents it; permissive intervention, under subdivision (b), is left to the court's discretion when the applicant's claim or defense shares a common question with the case.
When must a plaintiff notify the Attorney General under Rule 24?
Whenever the constitutionality of a Maine statute affecting the public interest is drawn into question in a case where the State of Maine or one of its officers or agencies is not already a party.
What must accompany a motion to intervene?
A pleading setting forth the claim or defense for which intervention is sought, along with the motion stating the grounds for intervention, served on the existing parties.
Source & verification. The rule text and Advisory Committee’s Notes / Reporter’s
Notes are reproduced verbatim from the official Maine Rules of Civil Procedure (Me. R. Civ. P. 24), prescribed by the
Supreme Judicial Court of Maine (4 M.R.S. § 8, the Rules Enabling Act). The plain-English summary is original and written by us. Last verified July 8, 2026. ·
Official source
Also known as: intervention of rightpermissive interventionstate intervening in constitutional challenge