Mont. Code § 85-7-2118
In any case where the board of commissioners of any irrigation district has made a levy or assessment under the provisions of 85-7-2104 through 85-7-2106 and included therein any amount due the United States under any contract or agreement for the purchase of any irrigation works or for the operation and maintenance of any irrigation works, while acting as fiscal agent for the United States, or under any authorization of the district by the United States to make collections of moneys for or on behalf of the United States in connection with any federal reclamation project, as provided in 85-7-1906, and the United States shall thereafter modify or supplement such contract or agreement so as to eliminate certain charges under said contract or agreement or so as to make such charges due at a later date or dates than originally provided in said contract or agreement, said board of commissioners are empowered to direct the cancellation of said levy or assessment theretofore made to raise funds to pay the United States that are under such modification or supplemental contract or agreement made due and payable at a later date or dates.
§ 85-7-2118, MCA