The Sixteenth Amendment to the U.S. Constitution empowered Congress to tax "incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration." The Internal Revenue Code is now embodied as Title 26 of the United States Code (26 U.S.C.) and was enacted following ratification of the Sixteenth Amendment.
All residents and all citizens of the United States are subject to the federal income tax. Not everyone, however, must file a return. The requirements for filing are found in 26 U.S.C. 6011. Corporations are also subject to federal income taxation under many of the same rules as individual taxpayers, they are also governed by a separate body of rules and regulations.
Certain income is exempt. For example, FICA generally does not have to be paid for sick pay received after a 6-month sick leave absence. Federal income tax rules are complex and constantly changing, so your tax professional should be consulted if you are uncertain about the applicabilty of the law to your tax liability.
