Mont. Code Ann. § 7-3-1318

Whenever for any cause the commission shall deem the bonds or securities of any bank insufficient security for the municipal funds deposited or likely to be deposited therein, the commission shall require new bonds to be given or new securities to be deposited with the treasurer. If any bank shall fail promptly to execute and present such new bonds or deposit such new securities, the treasurer shall at once withdraw all deposits therefrom, and no further deposit of municipal funds shall be made therein until such bank shall have been redesignated by the commission as a depository.