(1) Upon timely motion anyone shall be permitted to intervene in an action when the movant claims an interest relating to the property or transaction which is the subject of the action and the movant is so situated that the disposition of the action may as a practical matter impair or impede the movant’s ability to protect that interest, unless the movant’s interest is adequately represented by existing parties.
803.09.Intervention.
Ch. 803: Parties · Last amended 2017 · Last verified July 15, 2026
In one sentenceSection 803.09 lets anyone with an interest a lawsuit could impair intervene as of right unless existing parties adequately represent it, lets the court permit intervention when a claim or defense shares a common question with the case, and gives the legislature a right to intervene when a party challenges a statute’s validity.
Full Text of Section 803.09
(2) Upon timely motion anyone may be permitted to intervene in an action when a movant’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 or rule administered by a federal or state governmental officer or agency or upon any regulation, order, rule, requirement or agreement issued or made pursuant to the statute or executive order, the officer or agency upon timely motion 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. (2m) When a party to an action challenges in state or federal court the constitutionality of a statute, facially or as applied, challenges a statute as violating or preempted by federal law, or otherwise challenges the construction or validity of a statute, as part of a claim or affirmative defense, the assembly, the senate, and the legislature may intervene as set forth under s. 13.365 at any time in the action as a matter of right by serving a motion upon the parties as provided in s. 801.14.
(3) A person desiring to intervene shall serve a motion to intervene upon the parties as provided in s. 801.14. 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.
Plain-English Summary
On timely motion, anyone claiming an interest in the property or transaction at issue in a Wisconsin case must be permitted to intervene if the case’s disposition, without them, could as a practical matter impair or impede their ability to protect that interest, unless existing parties already adequately represent it. Separately, the court may permit intervention on timely motion when the movant’s claim or defense shares a question of law or fact with the main action, and a government officer or agency relying on a statute, executive order, rule, or related regulation it administers can seek that same permissive intervention; in deciding whether to allow it, the court considers whether intervention would unduly delay or prejudice the original parties’ rights.
When a party challenges a statute’s constitutionality, its validity under federal law, or its construction as part of a claim or affirmative defense, the assembly, the senate, and the legislature may intervene as a matter of right at any time by serving a motion on the parties.
A person seeking to intervene must serve a motion on the parties stating the grounds for intervention, accompanied by a pleading setting out the claim or defense for which intervention is sought, and the same procedure applies when a separate statute grants a right to intervene.
Frequently Asked Questions
When can someone intervene in a Wisconsin lawsuit as a matter of right?
When they claim an interest in the property or transaction at issue and the action’s disposition without them could, as a practical matter, impair their ability to protect that interest, unless existing parties already adequately represent it.
Can the court allow someone to intervene even without an interest that requires it?
Yes. Permissive intervention is available on timely motion when the movant’s claim or defense shares a common question of law or fact with the main action, and the court considers whether it would unduly delay or prejudice the case.
What does a motion to intervene have to include?
It must state the grounds for intervention and come with a pleading setting out the claim or defense for which intervention is sought, served on the parties.
Can the Wisconsin legislature intervene in a lawsuit challenging a statute?
Yes. If a party challenges a statute’s constitutionality, its validity under federal law, or its construction as part of a claim or defense, the assembly, senate, and legislature may intervene as a matter of right at any time.
Can a government agency intervene because a case involves a rule it administers?
Yes. An officer or agency relying on a statute, executive order, or related rule it administers may seek permissive intervention when its claim or defense shares a common question with the case.
Amendment History
History: Sup. Ct. Order, 67 Wis. 2d 585, 650 (1975); 1975 c. 218; 2007 a. 20; 2015 a. 55; 2017 a. 369.
Source & verification. Section text and official notes are
reproduced verbatim from the Wisconsin Statutes, published by the
Wisconsin Legislature (Legislative Reference Bureau). Last verified July 15, 2026.
· Official source
Also known as: intervention as of right wisconsinpermissive intervention wisconsin lawsuitlegislature intervening in a case wisconsinmotion to intervene requirements wisconsin