Any irrigation district now or hereafter organized under the laws of the state of Idaho and embracing lands subject to liens, charges or assessments for money owing the United States for water made available therefor through the construction of irrigation works, or otherwise, by the United States reclamation service, shall have power, through its board of directors, to extend the time for the payment of such indebtedness and to otherwise change and modify the time and manner of payment and the amount to be paid to the extent permitted under acts of congress and under any rule, regulation or contract of the department of the interior appertaining thereto and to that end the board of directors of any such district may amend or modify any existing contract with the United States or may enter into a new contract and may change, adjust, readjust and otherwise modify the liens, charges and assessments theretofore made against such lands and may cancel taxes theretofore levied by said irrigation district, including delinquent tax certificates still held by the district, and may do any and all things necessary to carry out such amended or new contract in accordance with such acts of congress: provided, that no contract with the United States for any of the purposes herein set forth shall be binding unless ratified by two-thirds (2/3) of the voters voting at an election to be held for that purpose in the manner provided by law for the ratification of contracts between irrigation districts and the United States.