Article II, Section 2, Clause 1:
The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States; he may require the Opinion, in writing, of the principal Officer in each of the executive Departments, upon any Subject relating to the Duties of their respective Offices, and he shall have Power to grant Reprieves and Pardons for Offences against the United States, except in Cases of Impeachment.
Congress cannot limit the effects of a presidential amnesty. Thus the act of July 12, 1870, making proof of loyalty necessary to recover property abandoned and sold by the government during the Civil War, notwithstanding any executive proclamation, pardon, amnesty, or other act of condonation or oblivion, was pronounced void. Chief Justice Chase wrote for the majority:
[T]he legislature cannot change the effect of such a pardon any more than the executive can change a law. Yet this is attempted by the provision under consideration. The Court is required to receive special pardons as evidence of guilt and to treat them as null and void. It is required to disregard pardons granted by proclamation on condition, though the condition has been fulfilled, and to deny them their legal effect. This certainly impairs the executive authority and directs the Court to be instrumental to that end.1 On the other hand, Congress itself, under the Necessary and Proper Clause, may enact amnesty laws remitting penalties incurred under the national statutes.2