Mont. Code Ann. § 13-27-306

A registered elector of a county having reason to believe that signatures on a petition that were not among those actually compared with signatures in the registration records of the county are not genuine may file a sworn statement or affirmation of the elector's belief and a request for comparison of those signatures that the elector believes are not genuine with the county official certifying the sheet or section of the petition. If any of the challenged signatures are not genuine, the county official shall compare all signatures on that sheet or section and issue an amended certificate to the secretary of state, giving the correct number of valid signatures, on or before the deadline, as provided for in 13-27-104, for filing in the office of the secretary of state.