United States coins and currency (including Federal reserve notes and circulating notes of Federal reserve banks and national banks) are legal tender for all de

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. Foreign gold or silver coins are not legal tender for debts. —31 U.S.C. § 5103 It seems unlikely that a prohibition on the use of cash in any transduction is likely to survive judicial examination.