Whenever there shall be filed with the commission any schedule stating a new individual or joint rate, fare, charge or classification for the transportation of passengers by a common carrier or carriers by motor vehicle, or by any such carrier or carriers in conjunction with a common carrier or carriers by railroad, express or water, or any rule, regulation or practice affecting such rate, fare or charge, or the value of the service thereunder, the commission is hereby authorized and empowered, upon complaint of any interested party or upon its own initiative, if it so orders, without answer or other formal pleading by the interested carrier or carriers, but upon reasonable notice, to enter upon a hearing concerning the lawfulness of such rate, fare or charge, or such rule, regulation or practice, and pending such hearing and the decision thereon the commission, by filing with such schedule and delivering to the carrier or carriers affected thereby, a statement in writing of its reasons for such suspension, may suspend the operation of such schedule and defer the use of such rate, fare or charge, or such rule, regulation or practice, for a period of ninety (90) days. If the proceeding has not been concluded and a final order made within such period, the commission may, from time to time, extend the period of suspension by order, but not for a longer period in the aggregate than one hundred eighty (180) days beyond the time when it would otherwise go into effect. After hearing, whether completed before or after the rate, fare, charge, classification, rule, regulation or practice goes into effect, the commission may make such order with reference thereto as would be proper in a proceeding instituted after it had become effective. If the proceeding has not been concluded and an order made within the period of suspension, the proposed change of rate, fare or charge, or classification, rule, regulation or practice shall go into effect at the end of such period.