First Republic Bank (FRC.N) fell about 30% on Thursday, leading shares of other regional lenders lower, as fears of a banking crisis loomed large.

The S&P 1500 regional banks sub-industry index (.SPCOMBNKS) slipped 1.8%, after tumbling more than 15% in the last four sessions, with some of its major constituents such as Western Alliance Bancorp (WAL.N) PacWest Bancorp (PACW.O) and KeyCorp (KEY.N) falling between 10% and 20%.

“Short sellers are attacking banks they think are weak, unfortunately First Republic has not done a very good job of pushing back. So the hedge funds keep attacking,” said Christopher Whalen, chairman at Whalen Global Advisors.

Short sellers have likely raked in $3.53 billion for the month as of March 14, with the bulk of it coming from the rout earlier this week, according to data from research firm S3 Partners.

The regional banking sector has been reeling from the collapse of Silicon Valley Bank on worries that nervous customers may rush to withdraw their deposits, potentially triggering a liquidity crisis.

Bloomberg reported on Wednesday that First Republic was weighing options to shore up its liquidity and that larger rivals might show interest in taking over the bank.

Several big banks, including JPMorgan Chase & Co (JPM.N) and Morgan Stanley (MS.N), are in talks with First Republic for a potential deal, the Wall Street Journal reported on Thursday.

“Regional banks are more Plain Jane and they do a lot more mortgage business and credit deposit business than say what a Citigroup does,” said Brad Lamensdorf, co-portfolio manager of Ranger Equity Bear ETF.

“So when you’re looking at regional banks, this net interest margin situation is much more damning.”

The U.S. Federal Reserve is expected to raise its main lending rate by 25 basis points next week.