Section 31 U.S.C. 5103, entitled "Legal tender," states: "United States coins and currency [including Federal Reserve notes and circulating notes of Federal Reserve Banks and national banks] are legal tender for all debts, public charges, taxes, and dues.
It states that Federal Reserve notes are legal tender, but it does not say that other notes or coins cannot be legal tender as well.
Before the Federal Reserve Act of 1913 we had the Coinage Act of 1792
The Coinage Act of 1792—more commonly known as the Mint Act or the Coinage Act—was a regulation passed by Congress on April 2, 1792, that established the United States Mint in Philadelphia. The act provided stipulations for the design and production of coins, laying the foundation for modern U.S. currency. The Coinage Act of 1792 outlined the duties of the five officers of the mint and established the U.S. dollar as the nation's standard unit of currency. https://www.investopedia.com/terms/c/the-coinage-act-of-1972.asp
The Coinage Act of 1792 instructed the U.S. mint to strike coins of gold, silver, and copper of various denominations.
Congress shall have power to borrow money on the credit of the United States. ~ Art. I, sec. 8, cl. 2.
Congress shall have power to coin money, regulate the Value thereof, and of foreign coin, and fix the standard of weights and measures. ~ Art. I, sec. 8, cl. 5.
Congress shall have power to provide for the punishment of counterfeiting the
securities and current coin of the United States. ~ Art. I, sec. 8, cl. 6.
No money shall be drawn from the Treasury, but in consequence of appropriations made by law. ~ Art. I, sec. 9, cl. 7.
The migration or importation of such persons as any of the states now existing shall think proper to admit, shall not be prohibited by the Congress prior to the year one thousand eight hundred and eight, but a tax or duty may be imposed on such
importation, not exceeding ten dollars for each person. ~ Art. I, sec. 9, cl. 1.
No state shall coin money, emit bills of credit, or make any thing but gold and silver coin a tender in payment of debts. ~ Art. I, sec. 10, cl. 1.
In suits at common law, where the value in controversy shall exceed twenty dollars, the right of trial by jury shall be preserved. ~ Amdt. VII.
The Constitution’s Five Monetary Rules
Read in conjunction with the Ninth and Tenth Amendments, and the obligation-of-contracts clause (Art. I, sec. 10, cl. 1), we can identify five monetary policies that are constitutionally requisite in the United States:
The basic unit is the dollar, a silver coin containing 371.25 grains of pure silver.
Only gold or silver coins and currency (specie-backed banknotes) can be legal tender.
No state may issue coins or currency.
No one may counterfeit U.S. Government-issued coins or currency.
Fiat money notes (‘bills of credit’) are forbidden.
According to monetary rule number five, the fiat federal reserve note is forbidden. However, the contracts clause in Article 1 section 10 could be argued as only applying to the states, not the federal government.
It states that Federal Reserve notes are legal tender, but it does not say that other notes or coins cannot be legal tender as well.
Before the Federal Reserve Act of 1913 we had the Coinage Act of 1792
The Coinage Act of 1792 instructed the U.S. mint to strike coins of gold, silver, and copper of various denominations.
There's seven clauses on money in the Constitution: Source: https://deanclancy.com/the-constitutions-seven-money-clauses/
Congress shall have power to borrow money on the credit of the United States. ~ Art. I, sec. 8, cl. 2.
Congress shall have power to coin money, regulate the Value thereof, and of foreign coin, and fix the standard of weights and measures. ~ Art. I, sec. 8, cl. 5.
Congress shall have power to provide for the punishment of counterfeiting the securities and current coin of the United States. ~ Art. I, sec. 8, cl. 6.
No money shall be drawn from the Treasury, but in consequence of appropriations made by law. ~ Art. I, sec. 9, cl. 7.
The migration or importation of such persons as any of the states now existing shall think proper to admit, shall not be prohibited by the Congress prior to the year one thousand eight hundred and eight, but a tax or duty may be imposed on such importation, not exceeding ten dollars for each person. ~ Art. I, sec. 9, cl. 1.
No state shall coin money, emit bills of credit, or make any thing but gold and silver coin a tender in payment of debts. ~ Art. I, sec. 10, cl. 1.
In suits at common law, where the value in controversy shall exceed twenty dollars, the right of trial by jury shall be preserved. ~ Amdt. VII.
The Constitution’s Five Monetary Rules
Read in conjunction with the Ninth and Tenth Amendments, and the obligation-of-contracts clause (Art. I, sec. 10, cl. 1), we can identify five monetary policies that are constitutionally requisite in the United States:
The basic unit is the dollar, a silver coin containing 371.25 grains of pure silver.
Only gold or silver coins and currency (specie-backed banknotes) can be legal tender.
No state may issue coins or currency.
No one may counterfeit U.S. Government-issued coins or currency.
Fiat money notes (‘bills of credit’) are forbidden.
According to monetary rule number five, the fiat federal reserve note is forbidden. However, the contracts clause in Article 1 section 10 could be argued as only applying to the states, not the federal government.