What cannot Congress tax?

Congress is prohibited from taxing exports based on the Constitution. This limitation is outlined in Article I, Section 9, where it states that "No tax or duty shall be laid on articles exported from any State." The reasoning behind this provision was to encourage free trade among the states and prevent the federal government from imposing burdens that could hinder interstate commerce.

While Congress has the power to impose taxes on imports and revenues, as well as personal income, the prohibition on export taxes means that goods shipped out from the U.S. cannot be taxed by Congress. This ensures that domestic producers are not disadvantaged in international markets compared to their competitors in other countries.