US securities regulators on Wednesday night said they would subpoena hedge funds for their past trading records and may force investors to disclose short sale positions, in the latest move to combat potential market manipulation.

The announcement followed another day of tumultuous trading in the stock market. Shares of Morgan Stanley and Goldman Sachs plunged and the cost of insuring their debt rose sharply – a sign of waning investor confidence in Wall Street’s last two large investment banks.