Federal regulators are tightening rules for money-market mutual funds to require them to hold some assets that could be easily converted to cash and to disclose new information on fund values.

The Securities and Exchange Commission voted Wednesday to adopt the new rules designed to bolster protection for investors in money-market funds, which hold about $3.2 trillion in assets.

The move came in response to an episode in September 2008, at the height of the financial crisis, in which a $60 billion money fund "broke the buck" and exposed investors to losses.

The value of the Primary Reserve Fund's assets fell to 97 cents per investor dollar — below the dollar-for-dollar level needed for full repayment.