Mont. Code Ann. § 7-15-4218

If the plan or any subsequent modification thereof involves financing by the issuance of general obligation bonds of the municipality as authorized in 7-15-4302 (1) or the financing of water or sewer improvements by the issuance of revenue bonds under the provisions of part 44 of chapter 7 or of part 43 of chapter 13, the question of approving the plan and issuing such bonds shall be submitted to a vote of the qualified electors of such municipality, in accordance with the provisions governing municipal general obligation bonds under chapter 7, part 42, at the same election and shall be approved by a majority of those qualified electors voting on such question.