"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."
http://caselaw.lp.findlaw.com/script...=240&invol=103
It was ruled by 3 judge panel of the supreme court in 1916 that the 16th amendment offered no new powers of taxation.
Since unappropriated income tax was not legal before the 16th amendment, it stands to logic it was not legal AFTER the 16th amendment in light of that ruling.
The fact is Income Tax is a VOLUNTARY system(it states so directly in the IRS code, which you can search).
There is no law requiring you to file taxes.
Now, the loophole to get around this is corporations are not protected entities and do not have any constitutional rights. The Tax code *requires* corporations to withhold a portion of employee's income before it is given to you(and thus is not in your possession at the time of taxation) to be given to the IRS.
This is "legal" because they are forcing an entity who has no rights to exercise their discretion of your employment, i.e. either you agree to follow the companies policy or they either fire/don't hire you, and the company has to have that policy because they're legally required to.