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 Oregon, the rules for intervention in a lawsuit are governed by state statutes and court rules. A person or entity, known as an intervenor, may seek to become a party to a lawsuit by filing a motion to intervene, typically before the court has entered a judgment. The right to intervene is granted if the potential intervenor has an interest that could have led them to initiate the same lawsuit or defend against it. The intervenor is not required to obtain permission from the court to intervene, but the existing party opposing the intervention can challenge it by filing a motion to strike. The court may be seen as abusing its discretion if it strikes an intervention when the intervenor meets the criteria of having a significant protectable interest, the intervention does not unduly complicate the case, and the intervention is necessary to protect the intervenor's interests. Oregon's rules are designed to ensure that parties with a direct stake in the outcome of a lawsuit have the opportunity to be heard, while also maintaining the efficiency and manageability of the legal proceedings.