577 Opinion of the Court. free time periods and of minimum charges to reflect the actual cost of services. 2 U. S. M. C. 588. Two of the terminal operators in the San Francisco Bay area were the State of California and the City of Oakland. They brought these proceedings to set aside the Commission's order in so far as it applied to them. A district court of three judges denied relief. 46 F. Supp. 474. The case is here on direct appeal under § 31 of the Shipping Act (c. 451, 39 Stat. 738, Ex. Ord. No. 6166, c. 858, 49 Stat. 1987, 2016, 46 U. S. C. § 830) in connection with the Urgent Deficiencies Act of 1913 (c. 32, 38 Stat. 220, 28 U. S. C. §§ 47 and 47a) and the Judiciary Act of 1925 (c. 229, 43 Stat. 938, 28 U. S. C. § 345 (4)). California and Oakland denied the power of the Commission to issue the kind of order that it did, and in any event they urged that the authority under which the Commission acted does not or, if it does, cannot constitutionally cover their operations. The legal issues depend for their solution upon an understanding of the situation to which the Commission addressed itself-the circumstances as the Commission found them and the appropriate way of dealing with them. What follows is a rapid summary of a voluminous record. Through its Board of State Harbor Commissioners, California provides facilities for the handling of freight and passengers on the San Francisco waterfront, under a statute which prohibits the Board from making charges beyond the cost of furnishing such facilities and administering them. California Harbors and Navigation Code §§ 3080, 3084. Pier and office space is assigned by the Board to various steamship lines, and charges fixed by the Board are collected by these assignees for the Board. Except at two piers, the assignees handle the cargo, but the Board employs a staff of men to check all cargo and vessel movements and collect its charges. Oakland, through its Board of Port Commissioners, operates Opinion of the Court. 320 U.S. piers and terminals which, like those of California, are designed to accommodate vessels in coastwise, intercoastal, offshore, and foreign trade. Whether the facilities are operated by the City directly or leased to another, the City prescribes and collects the charges. In thus providing facilities for water-borne traffic, Oakland and California have for many years competed with privately-owned terminals in San Francisco Bay. Cutthroat competition ensued, with the inevitable chaos following abnormally low rates. In an attempt to remedy the situation, the California Railroad Commission investigated the operations of terminals in San Francisco Bay, and, more particularly pertinent for present purposes, the prevalent discrimination among users of the terminal services. The conclusions from this inquiry were embodied in an order issued by the Railroad Commission in 1936. 40 Calif. R. R. Comm. Decisions 107. But publicly-owned terminals, and therefore those of California and Oakland, are not subject to the jurisdiction of the Railroad Commission. Since these public bodies operated the major portion of the dock facilities in the area, the Railroad Commission naturally found it impossible to order adjustments in the practices of the private terminals unless the competing public bodies agreed to make similar adjustments. The order of the Commission was so conditioned. California and Oakland acceded to the recommendations in some respects but failed to do so as to practices now to be described. When cargo is brought to a wharf for shipment or removed to a wharf from a ship, it is the custom to allow a period of "free time" during which the cargo may rest on the wharf without charge. The length of the free time is fixed, broadly speaking, by determining the period reasonably necessary for the shipper to assemble or to remove his goods and for the ship to load or to discharge. When cargo is left on the wharf beyond the free time period, a charge called "wharf demurrage or storage" is assessed. The Railroad Commission recommended free time periods shorter than was the practice of California and Oakland, and wharf demurrage charges greater in many instances than those collected by them. These recommendations California and Oakland rejected. This impasse, due to the immunity of California and Oakland from state regulation, was followed by the proceedings before the United States Maritime Commission which resulted in the order now before us. Extended hearings were held before the Commission's examiner, at which the principal witnesses were officials of the Board and Oakland and an expert of the Railroad Commission. After full submission of the controversy, the examiner made his report and findings. On exceptions to some of his findings, the issues were again thoroughly canvassed before the Commission, and on September 11, 1941, it made its order. The Commission found that there was a marked lack of uniformity in the free time periods allowed by the various terminals, and that to the extent that appellants' free time allowances were greater than those recommended by the Railroad Commission they were unreasonable and led to discrimination against those persons who did not and could not use extended free time. After consideration of the cost studies submitted by its experts as well as of the data introduced by appellants, the Commission further found that appellants' demurrage charges were less than the cost of the services and the carrying charges of the facilities which furnished them. It concluded that unless those who took advantage of wharf storage supplied revenue sufficient to meet the cost of the service, the burden would be shifted to those who paid appellants for other terminal services, such as docking of vessels, loading and unloading, and transportation privileges over and through the terminals. Accordingly, the Commission ordered appellants to cease and desist from allowing greater periods of free time than those found reasonable by the Railroad Commission, and to abstain from collecting wharf demurrage and storage rates less than those prescribed by the California authority for private terminals.2 Having found violations of §§ 16 and 17, the Commission was charged by law with the duty of devising appropriate means for their correction. It could have issued an order generally prohibiting further preferential and unreasonable practices, leaving the parties to translate such a generality into concreteness and to devise their own remedies. The Commission chose to do otherwise. It can hardly be suggested that the protection of the national interest in interstate and foreign commerce or even the convenience of the parties would, as a matter of sensible and economic administration, limit the Commission to such negative means of dealing with the evils revealed on this record in one of our greatest ports. Cf. Phelps Dodge Corp. v. Labor Board, 313 U. S. 177, 194. Explicit formulation of duties owed by a business subject to legal regulation is desirable if indeed not necessary. Only thus can it avoid the hazards of uncertainty whether its attempted compliance with an undefined requirement of law is in fact compliance. Neither industry nor the community which it serves is benefited by the explosion of intermittent lawsuits for determining the relative rights 2 The City of Oakland asks this Court to determine whether the Maritime Commission properly found that § 15 of the Shipping Act required Oakland to submit certain lease agreements for the Commission's approval. c. 451, 39 Stat. 733, Ex. Ord. No. 6166, c. 858, 49 Stat. 1987, 2016, 46 U. S. C. § 814. The Commission's order does not appear to require such filing. If this be an inadvertent or clerical omission, since Oakland's objection is founded on its basic contention that it is not subject to the Shipping Act, we need not further consider this subsidiary question. of conflicting interests. What more natural for the Commission, having found disobedience of the law against discriminatory and unreasonable practices, than to define the outer bounds of practices that would not be unreasonable nor discriminatory. And so the Commission fixed a schedule of maximum free time and another schedule for avoiding discrimination through non-compensatory charges. It acted on authoritative information and fully canvassed testimony in fixing the minimum charges that would reflect cost. It was proper to choose the cost standard, because just as unreasonably long free time tends to be parasitic on rates for other services, non-compensatory demurrage results in the same mischief. Cf. Baltimore & Ohio R. Co. v. United States, 305 U. S. 507, 524. Appellants' objection is that while §§ 17 and 18 specifically give the Commission rate-making power over common carriers by water,* no such power is given over those & Booth S. S. Co. v. United States, 29 F. Supp. 221, is an object lesson. In that case, the order of the Maritime Commission as to the charges to be imposed after free time was in general terms. Attempted compliance with that order led to conflict, and the Commission found it necessary to undertake new proceedings and to issue a new, more definite order. The following are the rate provisions in §§ 17 and 18. Section 17: "That no common carrier by water in foreign commerce shall demand, charge, or collect any rate, fare, or charge which is unjustly discriminatory between shippers or ports, or unjustly prejudicial to exporters of the United States as compared with their foreign competitors. Whenever the commission finds that any such rate, fare, or charge is demanded, charged, or collected it may alter the same to the extent necessary to correct such unjust discrimination or prejudice and make an order that the carrier shall discontinue demanding, charging, or collecting any such unjustly discriminatory or prejudicial rate, fare, or charge." Section 18: "That every common carrier by water in interstate commerce shall establish, observe, and enforce just and reasonable rates, fares, charges, classifications, and tariffs, and just and reasonable regulations and practices relating thereto. . . . Whenever the commission finds that any rate, fare, charge, classification, |