From 26 USC 1:
"There is hereby imposed on the taxable income of every individual..."
(refer to http://www.law.cornell.edu/uscode/text/26/1 for more details).
From Black's Law Dictionary 9th (2009):
impose, vb. (l7c) To levy or exact (a tax or duty).
levy, vb. (l4c) 1. To impose or assess (a fme or a tax) by legal authority <levy a tax on gasoline>. 2. To enlist for service in the military <the troops were quickly levied>. 3. To declare or wage (a war) <the rival clans levied war against each other>. 4. To take or seize property in execution of a judgment <the judgment creditor may levy on the debtor's assets>. [Cases: Execution C=> 122-147.]
From Blacks Law Dictionary 2nd (1910):
IMPOSITION. An impost; tax; contribution. Paterson v. Society, 24 N. J. _Law,
400; Singer Mfg. Co. v. Heppenbeimer, 58 N. J .. Law, 633, 34 Atl. 1061, 32 L. R. A.. 643.
LEVY, n.. In practice. A seizure ; the raising of the money for which an execution
has been· issued.
LEVY, v. To raise ; execute ; exact; collect; gather; take up; seize. Thus, to levy
(raise or collect) a tax ; to levy (raise or setup) a nuisance; to levy (acknowledge) a fine; to levy (Inaugurate) war ; t.o levy an execution, i.e., to levy or collect a sum of money on an execution.
TAX, n. Taxes are a ratable portion of 'the produce of the property and labor of that Individual· citizens, taken by the nation, in the exercise of Its sovereign rights, for the support of government, for the administration of the laws, and as the means for continuing in operation the various legitimate functions of the state. Black, Tax Titles, I 2; ·New London v. Miller, 60 Conn. 112, 22 Atl. 499 ; Graham v. St. Joseph Tp., 67 Mich. 652, 85 .N. w. 808 ; · Gibbons v. Ogden, 9 Wheat. 1, 6 L. Ed. 23.
By the way, to whom does 26 USC 6065 apply, and why?