Sixteenth Amendment to the United States Constitution
Amendment XVI (the Sixteenth Amendment) of the United States Constitution, authorizing a graduated income tax, was ratified on February 3, 1913. It states: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.
Interpretation and history
Congress had previously attempted a federal income tax which was declared unconstitutional in 1895 as a "direct tax", forbidden by Article I of the Constitution. In response, this amendment was passed in order to make federal income taxes constitutional.There is some academic dispute as to whether proper procedure was followed in the ratification of this amendment.
http://www.archives.gov/exhibit_hall/charters_of_freedom/constitution/amendments_11-27.html#16
