A municipality has the power and authority to regulate, establish, and change, as it considers proper, rates, charges, and classifications imposed for utility services to its inhabitants and other persons served by municipal utility systems. Rates, charges, and classifications must be reasonable and just.
Municipal Utilities -- Regulation By Municipality
Mont. Code Ann. § 69-7-101, under Regulation of Rates by Municipality.
Mont. Code Ann. § 69-7-101