Mont. Code Ann. § 25-33-203

The adverse party may except to the sufficiency of the sureties within 5 days after the filing of the undertaking, and unless they or other sureties justify before the justice or a judge of the district court of the county in which such action has been tried within 5 days thereafter, upon notice to the adverse party, to the amounts stated in their affidavits, the appeal must be regarded as if no such undertaking had been given. The sureties on the undertakings mentioned in this part must justify as provided in 33-26-102.