Idaho Code § 61-308

The names of the several public utilities which are parties to any joint tariff, rate, fare, toll contract, classification or charge shall be specified in the schedule or schedules showing the same. Unless otherwise ordered by the commission, a schedule showing such joint tariff, rate, fare, toll, contract, classification or charge need be filed with the commission by only one (1) of the parties to it: provided, that there is also filed with the commission in such form as the commission may require a concurrence in such joint tariff rate, fare, toll, contract, classification or charge by each of the other parties thereto.