The 16th Amendment removed the Constitutional control that the Founding Fathers required for Federal Direct Income Taxes. The Founding Fathers wanted Direct Taxes to be only levied according to the census. The 16th Amendment gave Congress complete and arbitrary power to tax incomes from whatever source derived without regards to the CENSUS.
Myself and many others have called this the "Blank Check Amendment" The repeal of the 16th Amendment is the single most effective way to control Congress' run away deficit spending.