2-408.Intervention.

Some applicants get to intervene as of right: when a statute gives an unconditional right to intervene, when the existing parties' representation of the applicant's interest is or may be inadequate and the applicant will or may be bound by the outcome, or when the applicant would be adversely affected by how the court or a court officer disposes of property in its custody or control. Other applicants intervene only at the court's discretion — when a statute gives a conditional right, or when the applicant's claim or defense shares a question of law or fact with the main action. The State can seek discretionary intervention in cases testing the validity of a state constitutional provision, statute, or regulation that affect the public interest, and a municipality or other governmental subdivision can do the same for cases testing the validity of its own ordinances or regulations.

Anyone seeking to intervene files a petition stating the grounds for intervention, along with the pleading or motion they propose to file if allowed in. Where intervention is discretionary, the court weighs whether it will unduly delay or prejudice the resolution of the original parties' rights.

An intervenor generally gets all the rights of an original party. But the court's order allowing intervention — whether granted as of right or as a matter of discretion — can limit that: binding the intervenor to orders, judgments, or evidence already in the case, barring the intervenor from raising issues that should have come up earlier, barring new issues or new parties, or otherwise keeping the intervenor from interfering with how the litigation is run, as justice and avoiding undue delay require.