The Constitution and laws passed by Congress have given the U.S. government authorization to collect various taxes. For example, duties are taxes imposed upon imports and can be either advalorem (a percentage of the value of the property) or specific (a fixed amount). An impost is another name for an import tax. Congress may not, however, tax exports.
The SIXTEENTH AMENDMENT to the Constitution gives Congress the power to impose a federal income tax. Congress has also enacted laws that allow the federal government to tax estates remaining after people die and gifts made while people are alive.