According to the SCOTUS, the income tax is an excise tax. Interestingly enough, an excise is imposed on the exercise of a granted privilege. So working for a living is a privilege, granted by Congress and presumably able to be withdrawn by Congress for any, or no, reason. 
According to the SCOTUS, the income tax is an excise tax. Interestingly enough, an excise is imposed on the exercise of a granted privilege.
According to SCOTUS, an excise is a tax on any activity, whether on privilege or not.
Charles C. Stewart Machine Co. v. Davis (1937), 301 U.S. 548:
- "But natural rights, so called, are as much subject to taxation as rights of lesser importance. An excise is not limited to vocations or activities that may be prohibited altogether. It is not limited to those that are the outcome of a franchise. It extends to vocations or activities pursued as of common right."
- Employment is a business relation, if not itself a business. It is a relation without which business could seldom be carried on effectively. The power to tax the activities and relations that constitute a calling considered as a unit is the power to tax any of them. The whole includes the parts. Nashville, C. & St. L. Ry. Co. v. Wallace, 288 U.S. 249, 267 , 268 S., 53 S.Ct. 345, 349, 350, 87 A.L.R. 1191
KNOWLTON v. MOORE, 178 U.S. 41 (1900)
- 'indirect taxes are levied upon the happening of an event or an exchange.'
Tyler v. U.S. 281 U.S. 497, 502 (1930)
- An indirect tax is a tax laid upon the happening of an event,as distinguished from its tangible fruits.
U.S. v. CONSTANTINE, 296 U.S. 287 (1935)
- " The United States has the power to levy excises upon occupations, and to classify them for this purpose; and need look only to the fact of the exercise of the occupation or calling taxed, regardless of whether such exercise is permitted or prohibited by the laws of the United States or by those of a state. The burden of the tax may be imposed alike on the just and the unjust."