But, further, under this concurrent power, the State does that which Congress cannot do; that is, it gives preferences to the citizens of some States over those of others.  I do not mean here the advantages conferred by the grant on the grantees; but the disadvantages to which it subjects all the other citizens of New York.  To impose an extraordinary tax on steam navigation visiting the ports of New York, and leaving it free everywhere else, is giving a preference to the citizens of other States over those of New York.  This Congress could not do; and yet the State does it; so that this power, at first subordinate, then concurrent, now becomes paramount.

The people of New York have a right to be protected against this monopoly.  It is one of the objects for which they agreed to this Constitution, that they should stand on an equality in commercial regulations; and if the government should not insure them that, the promises made to them in its behalf would not be performed.

I contend, therefore, in conclusion on this point, that the power of Congress over these high branches of commercial regulation is shown to be exclusive, by considering what was wished and intended to be done, when the convention for forming the Constitution was called; by what was understood, in the State conventions, to have been accomplished by the instrument; by the prohibitions on the States, and the express exception relative to inspection laws; by the nature of the power itself; by the terms used, as connected with the nature of the power; by the subsequent understanding and practice, both of Congress and the States; by the grant of exclusive admiralty jurisdiction to the federal government; by the manifest danger of the opposite doctrine, and the ruinous consequences to which it directly leads.

Little is now required to be said, to prove that this exclusive grant is a law regulating commerce; although, in some of the discussions elsewhere, it has been called a law of police.  If it be not a regulation of commerce, then it follows, against the constant admission on the other side, that Congress, even by an express act, cannot annul or control it.  For if it be not a regulation of commerce, Congress has no concern with it.  But the granting of monopolies of this kind is always referred to the power over commerce.  It was as arbiter of commerce that the king formerly granted such monopolies.[4] This is a law regulating commerce, inasmuch as it imposes new conditions and terms on the coasting trade, on foreign trade generally, and on foreign trade as regulated by treaties; and inasmuch as it interferes with the free navigation of navigable waters.

If, then, the power of commercial regulation possessed by Congress be, in regard to the great branches of it, exclusive; and if this grant of New York be a commercial regulation, affecting commerce in respect to these great branches, then the grant is void, whether any case of actual collision has happened or not.