Moody’s Investors Service is weighing a credit downgrade for six U.S. banks following the second- and third-largest bank failures in the nation’s history.

The credit rating firm said Monday that the regional banks are “exposed to the risk of uninsured deposit outflows” in the wake of Silicon Valley Bank collapse, which prompted fears that wealthy depositors might move their money to larger institutions. 

Moody’s will review ratings for San Francisco’s First Republic Bank, Phoenix-based Western Alliance Bancorporation, Dallas-based Comerica Bank, Kansas City’s UMB Financial, Utah’s Zions Bank and Wichita-based Intrust Financial.

The firm said that First Republic Bank has substantial unrealized losses on its investments and a low level of capitalization compared to its peers. Because the bank has a “material” share of deposits that are above the Federal Deposit Insurance Corporation’s (FDIC) $250,000 insurance limit, it faces an elevated risk of rapid and large withdrawals, according to Moody’s.

“If it were to face higher-than-anticipated deposit outflows and liquidity backstops proved insufficient, the bank could need to sell assets, thus crystallizing unrealized losses on its [securities],” Moody’s analysts wrote. 

Regional banks’ shares saw huge selloffs on Monday before recovering the next day. First Republic’s shares plummeted 62 percent on Monday, then rose 49 percent on Tuesday. 

Federal regulators shuttered San Francisco’s Silicon Valley Bank following a bank run from its tech-focused clients who were concerned about the bank’s hefty unrealized losses on long-term treasury bonds, which took a hit due to the Federal Reserve’s interest rate hikes.

Regulators also closed down New York’s Signature Bank and guaranteed that depositors at both banks would get their money back through a fund that is paid for by fees on banks. The Fed launched an emergency lending program to make sure banks have enough cash to fulfill withdrawals.

Moody’s analysts noted that the Fed program is an “offset to these funding risks.”