Federalist 36: 10
Let it be recollected that the proportion of these taxes is not to be left to the discretion of the national legislature, but is to be determined by the numbers of each State, as described in the second section of the first article. An actual census or enumeration of the people must furnish the rule, a circumstance which effectually shuts the door to partiality or oppression. The abuse of this power of taxation seems to have been provided against with guarded circumspection. In addition to the precaution just mentioned, there is a provision that "all duties, imposts, and excises shall be UNIFORM throughout the United States.''
Article 1 Section 8: 1
The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States;
Article 1 Section 8: 4
To establish an uniform Rule of Naturalization, and uniform Laws on the subject of Bankruptcies throughout the United States;
Article 1 Section 9: 4
No Capitation, or other direct, Tax shall be laid, unless in Proportion to the Census or Enumeration herein before directed to be taken.
Article 1 Section 10: 2
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 it's 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 Controul of the Congress.
Article 2 Section 1: 4
The Congress may determine the Time of chusing the Electors, and the Day on which they shall give their Votes; which Day shall be the same throughout the United States.
Article 5: 1
... or by Conventions in three fourths thereof, as the one or the other Mode of Ratification may be proposed by the Congress; Provided that no Amendment which may be made prior to the Year One thousand eight hundred and eight shall in any Manner affect the first and fourth Clauses in the Ninth Section of the first Article; and that no State, without its Consent, shall be deprived of it's equal Suffrage in the Senate.
Amendment 16: 1
The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration.