What is a power regarding taxation that Congress cannot exercise?

The power regarding taxation that Congress cannot exercise is the taxation of exports from any state. This restriction is rooted in Article I, Section 9 of the U.S. Constitution, which explicitly prohibits the federal government from imposing taxes on goods exported from states. This provision was included to protect state economies and promote free trade among states. By ensuring that exports are not taxed at the federal level, it encourages trade and commerce beyond state boundaries.

In contrast, Congress has the authority to tax income, corporate profits, and capital gains, as these types of taxation are essential for federal revenue generation and are considered a part of the government's power to regulate the economy. Since exports are exempt from federal taxation, it highlights the importance of maintaining balance in economic interactions between states and the federal government.