Mont. Code Ann. § 27-28-301

A person claiming to be entitled to a public office unlawfully held and exercised by another, individually or by an attorney, may bring an action for the office in the name of the state, as provided in this chapter. On filing the complaint, the person shall enter into an undertaking, with two sufficient sureties to be approved by the judge or any judge of the court in which the action is brought, conditioned that the person will pay any judgment for costs or damages recovered against the person and all costs and expenses incurred in the prosecution of the action. The undertaking must be filed with the clerk of the court.