Mont. Code Ann. § 18-2-202

If any board, council, commission, trustee, or body acting for the state or any board of county commissioners or any mayor and common council of any incorporated city or town or tribunal transacting the business of any such municipal corporation waives or fails to take the security required or authorized by 18-2-201, the state or the county, incorporated city or town, or other municipal corporation is liable to the persons mentioned in 18-2-201 to the full extent and for the full amount of all of the contracted debts by any subcontractor as well as the contractor.