A preliminary outline is essential to clear the way for an understanding of the case. By original action here brought, the state sues to tecover a sum of money for passenger fares in excess of the rate established by law, paid by its officers when traveling within the state, on state business. Answering, the railroad alleges among other defenses that the rates fixed by law were so low as to be confiscatory, and hence repugnant to the Constitution of the United States. The matter for decision arises on a motion on behalf of the state to strike out this defense on the ground that the right to assert it is barred by a decree of this court, establishing that the rates fixed by the state law were lawful, and not confiscatory,-a decree the conclusive effect of which, it is asserted, the railroad company is estopped from denying.
The case as made by the pleadings and by the record in which the decree relied on was rendered, of which we take judicial notice, is this: In April, 1905, by law, Missouri established certain freight rates. Almost at once the defendant company and others filed their bills in the circuit court of the United States for the western district of Missouri against the State Board of Warehouse Commissioners, the attorney general of the state, and certain shippers, alleged to be representative, to enjoin the carrying out of the rate-fixing law on the ground that to enforce the rates which it fixed would result in confiscation and a taking of the property of the railroads in violation of the Constitution. An injunction was granted prohibiting the carrying into effect of the rate law. While these suits were pending, the state by law fixed a passenger rate, and, repealing the freight law which had been enjoined, enacted another, and by supplemental bills both these laws were assailed on the grounds upon which the other law had been attacked, and injunctions were awarded restraining their enforcement. After much testimony offered on the issue of confiscation, the court permanently enjoined the enforcement of the state statutes. On review in this court, as to the railroad now before us and others, this conclusion was held to be erroneous, and the decree which was entered here reversed and remanded the case, with directions to dismiss the bill, without prejudice. Missouri Rate Cases (Knott v. Chicago, B. & Q. R. Co.) 230 U.S. 474, 509, 57 L. ed. 1571, 1595, 33 Sup. Ct. Rep. 975.
Although the contentions respectively pressed in argument are numerous, their solution depends upon the application of a few well-settle principles which we proceed to state in order to test all the propositions by applying them, and thus avoid redundancy.
1. In Chicago, M. & St. P. R. Co. v. Minnesota, 134 U.S. 418, 33 L. ed. 970, 3 Inters. Com. Rep. 209, 10 Sup. Ct. Rep. 462, 702, considering a law fixing railroad rates in the light of two settled rules, (a) that, in exerting the public rate-making power, the rates cannot be made so low as to be confiscatory, without violating the Constitution, and (b) that although a state is not subject to suit without its consent, there is always the right to enjoin an individual, whether he is a state officer or not, from doing an act violating the Constitution, that is, from taking property unlawfully, it was held that both these propositions controlled in the fullest degree in the legislative fixing of railroad rates. In fact it was in that case decided that from the act of fixing railroad rates by law there resulted the duty to provide an opportunity for testing their repugnancy as a unit to the Constitution in case there was a charge that they were confiscatory. It was accordingly held that, in virtue of the due process of law provision of the 14th Amendment, the state could not by mandamus compel a railroad to comply with rates fixed by a state law unless an opportunity was afforded to test the question of confiscation.