The federal Constitution lays but one express limitation upon the States with reference to the exercise of their taxing powers. This is that "no State shall, without the consent of the Congress, lay any imposts or duties on imports or exports, except what may be absolutely necessary for executing the inspection laws; and the net produce of all duties and imposts, laid by any State on imports or exports, shall be for the use of the Treasury of the United States, and all such laws shall be subject to the revision and control of the Congress." 1

But other clauses of the Constitution restricting generally the powers of the States operate to limit their powers of taxation. Thus, for example, influential in this respect are the provisions that no State shall deprive any person of property without due process of law or deny to any person within its jurisdiction the legal protection of the laws; that no State shall pass any law impairing the obligation of contracts; and that "the citizens of each State shall be entitled to all privileges and immunities of citizens in the several States." Also there are the implied limitations that no State shall so use its taxing powers as to interfere with the operation of federal agencies; and that, being unable to give an extraterritorial effect to its laws, no State may tax property not within its jurisdiction.

The limitations imposed upon the taxing powers of the States by the "comity" clause2 are discussed in chapter XII (Interstate Relations; Full Force And Credit Clause. 91. States Independent Of One Another) of this treatise. It may, however, be here said that, in general, the clause operates to prevent a State from burdening citizens of other States within its borders with heavier taxes than those laid upon its own citizens. This applies not only to the property of non-citizens but to the business that they may carry on.3

1 Art. I, Sec. X, CI. 2. 2 Art. IV, § 2, CI 1.