A person or entity who is not a party to a lawsuit generally may intervene in the lawsuit and become a party to it by filing a plea in intervention prior to the entry of the court’s judgment—provided the court does not reject (strike) the intervention. An intervenor is not required to secure the court’s permission to intervene, and the party who opposed the intervention has the burden to challenge it by filing a motion to strike.

A person or entity has a right to intervene if the intervenor could have brought the same lawsuit, or any part of it in his own name—or, if the action had been brought against him, he would be able to defeat the lawsuit, or some part of it.

A trial court abuses its discretion by striking an intervention if (1) the intervenor meets the above test, (2) the intervention will not complicate the case by an excessive multiplication of the issues, and (3) the intervention is almost essential to effectively protect the intervenor’s interest.

In Iowa, the rules regarding intervention in a lawsuit are governed by the Iowa Rules of Civil Procedure. A person or entity, known as an intervenor, may join an ongoing lawsuit without needing to obtain permission from the court by filing a plea in intervention before the court enters its judgment. The intervenor must have a significant interest in the case, such that they could have initiated the same lawsuit themselves or would have a defense against the lawsuit if it were brought against them. The party opposing the intervention bears the responsibility to challenge it by filing a motion to strike. The court may only strike the intervention if it does not meet the criteria of the intervenor being able to bring or defend against the lawsuit, if the intervention does not excessively complicate the case, and if the intervention is necessary to protect the intervenor's interests. If a trial court strikes an intervention that meets these conditions, it may be considered an abuse of discretion.