The Constitution gives Congress all its legislative powers. Section 8 of Article I gives the Congress its specific enumerated powers: "the Congress shall have power to lay and collect taxes, duties, imposts, and excises, to pay the debt and provide for the common defense and general welfare of the United States; but all duties, imposts, and excises shall be uniform throughout the United States.".
The first responsibility of Congress is taxation. Over the years, Congress has imposed various forms of tax, from import duties to income taxes. Throughout American history, taxation has remained one of the most controversial aspects of congressional power, No one likes to pay taxes, and finding the proper balance in tax policy has always been difficult. During most of the nineteenth century, the level and function of tariffs were highly debated. In the twentieth century, the issues have usually revolved around the rate of income taxes.
The Constitution places four explicit limits on the type of taxes that can be imposed. First of all, taxes can only be imposed for the common good. Tax revenue can be used to pay the debt, and provide for the common defense and general welfare of the United States. Secondly, no taxes on exports are allowed. The third limitation is that direct taxes must be apportioned to the states according to their population. A direct tax is any tax that is imposed directly on the people that pay it--for example, an income tax or a poll tax. However, the Sixteenth Amendment removes the third limitation from income taxes. Finally, all duties imposts and excises must be uniform throughout the United States.