The public utilities commission may, and on complaint shall, investigate any freight rates on interstate traffic on railroads in this state. If in its opinion they are excessive, discriminatory, levied in violation of the interstate commerce law, or in conflict with the rulings, orders, or regulations of the interstate commerce commission, it shall present the facts to the railroad with the request to make such changes as the public utilities commission advises. If such changes are not made within a reasonable time, the public utilities commission shall apply by petition to the interstate commerce commission for relief.