There is no federal law requiring a private business—including a bank branch—to accept any specific denomination of currency for a transaction, although this is rare. While currency is "legal tender for all debts, public and private," this does not mean that every private entity must accept a $50 bill for every interaction. In the context of a bank, if you are making a deposit, they will almost always accept a $50 bill. However, if you are attempting to exchange currency or perform a transaction where the bank has specific internal policies about currency condition or supply, they might theoretically refuse. It is extremely uncommon for a bank to refuse a standard $50 bill, as their business is the intake and distribution of cash. If they refuse, it is likely due to a specific policy related to suspicious currency or a temporary shortage of denominations needed for their internal operational requirements.