Whenever the commission, after hearing had on reasonable notice, finds that the existing rates in effect and collected by any public utility are unjust, unreasonable, materially excessive or insufficient or unreasonably discriminatory, or in anywise in violation of any provision of law, the commission shall determine, and fix by order, the just and reasonable rates which will yield a fair rate of return to the utility for furnishing service, which rates will thereafter be observed and in force. Said rates shall thereupon become the legal rates to be charged and paid until changed.
The commission shall have power, when deemed by it necessary to prevent injury to the business or interest of the people or any public utility of this state in case of any emergency, to permit any public utility to alter, amend or suspend temporarily any existing rates, schedules and orders relating to or affecting any public utility or part of any public utility in this state except as provided in Section 77-3-42.