A growing number of big U.S. credit-card issuers are deciding they don’t want to finance a falling knife.

JPMorgan Chase & Co. and Bank of America Corp., the nation’s two largest banks, said they’re halting purchases of Bitcoin and other cryptocurrencies on their credit cards. JPMorgan, which will implement the ban Saturday, doesn’t want the credit risk associated with the transactions, said Mary Jane Rogers, a spokeswoman for the firm.

Bank of America told staff in a memo that it will start declining credit card transactions with known crypto exchanges today. The policy applies to all personal and business credit cards issued by the bank. The move doesn’t affect debit cards, according to Betty Riess, a spokeswoman for the Charlotte, North Carolina-based lender.

Allowing purchases of cryptocurrencies can create big headaches for card lenders, which can be left on the hook if a borrower bets wrong and can’t repay. Banks also are required by regulators to monitor customer transactions for signs of money laundering.

But cutting off card purchases has big implications for Bitcoin and other virtual currencies, potentially making it more difficult for an enthusiastic public to jump into that market.

Citigroup Inc., the nation’s third-biggest bank, is still reviewing its policy. Capital One Financial Corp. and Discover Financial Services previously said they aren’t supporting the transactions.

Discover Chief Executive Officer David Nelms was dismissive of financing cryptocurrency transactions during an interview last month, noting that could change depending on customer demand. For now, “it’s crooks that are trying to get money out of China or wherever,” he said of those trying to use the currencies.