Income tax is an Indirect Tax

"In the matter of taxation, the Constitution recognizes the two great classes of direct and indirect taxes, and lays down two rules by which their imposition must be governed, namely: The rule of apportionment as to direct taxes and the rule of uniformity as to duties, imposts and excises." Pollock v. Farmers' Load & Trust Co., 157 U.S. 429, at 557 (1895); and Brushaber v. Union Pacific R.R. Co., 240 U.S. 1, at 13. (1916)

"The income tax is, therefore, not a tax on income as such.  It is an excise tax with respect to certain activities and privileges which is measured by reference to the income which they produce.  The income is not the subject of the tax:  it is the basis for determining the amount of tax. House Congressional Record, March 27, 1943, page 2580.

"The contention that the Amendment [16th] treats a tax on income as a direct tax ... is ... wholly without foundation."Brushaber v. Union Pacific R.R. Co., 240 U.S. 1, at page 18. (1916)

"The conclusion reached in the Pollock Case did not in any degree involve the holding that income taxes generically and necessarily came within the class of direct taxes on property, but on the contrary recognized the fact that taxation on income was in its nature an excise entitled to be enforced as such..."Brushaber, supra, at pages 16-17.

"[B]y the previous ruling {Brushaber Case] it was settled that the Sixteenth amendment conferred no new power of taxation but simply prohibited the previous complete and plenary power of income taxation possessed by Congress from the beginning from being taken out of the category of indirect taxation to which it inherently belonged…Stanton v. Baltic Mining Co., 240 U.S. 103 at 112 (1916)"