Whenever pursuant to § 56-237 there shall be filed with the Commission any schedule required to be filed under § 56-236 stating a change of rate, toll or charge and a protest or objection thereto is filed by or on behalf of the lesser of 150 or five percent of the customers or consumers or other persons subject to such rate, toll or charge, the Commission shall upon reasonable notice conduct a public hearing concerning the lawfulness of the proposed rate, toll or charge. At any such hearing involving a change of such rate, toll or charge, the burden of proof shall be upon the applicant therefor to demonstrate that the proposed change is just and reasonable. The Commission shall prescribe all necessary rules and regulations for the conduct of such hearing, which rules shall afford ample opportunity for participation or representation by persons affected by such change.