Whenever discriminatory, unreasonable, or unjust, rates, rules, or practices on interstate business are not changed or adjusted so as to remove or remedy the discrimination, unreasonableness, or unjustness, within a reasonable time, the commission shall take the action necessary in an appropriate proceeding to obtain relief from such rates, rules, or practices. If the commission deems it necessary, the attorney general, with such other assistance as may be provided by law, shall prosecute any charge growing out of any such discrimination.