Exclusive federal powers are powers within a federal system of government that each constituent political unit (such as a state or province) is absolutely or conditionally prohibited from exercising. That is, either a constituent political unit may never exercise these powers, or may only do so with the consent of the federal government.
These powers are contrasted with concurrent powers, which are shared by both the federal government and each constituent political unit. They are also contrasted with powers belonging exclusively to each constituent political unit, sometimes called states' rights.
According to U.S. law, reserved powers (i.e. states' rights) belong exclusively to each state. They are distinct from the enumerated powers that are listed in the Constitution of the United States, which include both concurrent powers and exclusive federal powers.
In Federalist No. 32, Alexander Hamilton described three distinct types of exclusive federal powers:
This exclusive delegation, or rather this alienation, of State sovereignty, would only exist in three cases: [i] where the Constitution in express terms granted an exclusive authority to the Union; [ii] where it granted in one instance an authority to the Union, and in another prohibited the States from exercising the like authority; and [iii] where it granted an authority to the Union, to which a similar authority in the States would be absolutely and totally contradictory and repugnant.
Hamilton proceeded to give examples of all three types. As to express exclusivity [i], the Constitution grants Congress power of "exclusive legislation" over the area now known as the District of Columbia. As to express prohibition [ii], the Constitution says: "no state shall, without the consent of Congress, lay any imposts or duties on imports or exports, except for the purpose of executing its inspection laws." And, as to repugnancy [iii], the Constitution gives Congress power to establish a "uniform rule" of naturalization throughout the country, and Hamilton says that there could be no uniform rule if each state has a distinct rule.
Regarding Hamilton's repugnancy example [iii], the U.S. Supreme Court has said that the Constitution's requirement of a "uniform" bankruptcy law does not preclude distinct bankruptcy rules in each state, assuming the state legislation does not extend to "that part of the subject to which the acts of Congress may extend". However, the Court has also said that the naturalization power of Congress is exclusive.