(a) When a tariff filing is made containing a new or revised rate, classification, rule, regulation, practice, or condition of service the commission may, either upon written complaint or upon its own motion, after reasonable notice, conduct a hearing to determine the reasonableness and propriety of the filing. Pending the hearing the commission may, by order stating the reasons for its action, suspend the operation of the tariff filing. For a tariff filing that does not change the utility's revenue requirement or rate design, the suspension may last for a period not longer than six months beyond the effective date established in the tariff filing unless the commission extends the period for good cause. For a tariff filing that changes the utility's revenue requirement or rate design, the suspension may last, unless the commission extends the period for good cause, for a period not longer than

(1) six months before an interim rate equal to the requested rate goes into effect and not longer than 12 months before a permanent rate goes into effect if the annual gross revenues of the utility making the filing are more than $3,000,000; and

(2) 150 days before an interim rate equal to the requested new rate goes into effect and not longer than one year before a permanent rate goes into effect if the annual gross revenues of the utility making the filing are $3,000,000 or less.

(b) An order suspending a tariff filing may be vacated if, after investigation, the commission finds that it is in all respects proper. Otherwise the commission shall hold a hearing on the suspended filing and issue its order, before the end of the suspension period, granting, denying or modifying the suspended tariff in whole or in part.

(c) In the case of a proposed increased rate, the commission may by order require the interested public utility or utilities to place in escrow in a financial institution approved by the commission and keep accurate account of all amounts received by reason of the increase, specifying by whom and in whose behalf the amounts are paid. Upon completion of the hearing and decision the commission may by order require the public utility to refund to the persons in whose behalf the amounts were paid, that portion of the increased rates which was found to be unreasonable or unlawful. Funds may not be released from escrow without the commission's prior written consent and the escrow agent shall be so instructed by the utility, in writing, with a copy to the commission. The utility may, at its expense, substitute a bond in lieu of the escrow requirement.

(d) One who initiates a change in existing tariffs shall bear the burden to prove the reasonableness of the change.