A hallmark of the $18 trillion mutual-fund industry is that itpromises easy entry and exit for investors. U.S. regulators nowwant new protections to ensure that pledge can be met, due toconcerns that firms have loaded up on hard-to-sell assets.

The five-member Securities and Exchange Commission (SEC) votedunanimously to pass a measure Tuesday that addresses criticismsthat its rules haven't kept pace with the evolution of the fundindustry. The SEC's proposal follows warnings from the FederalReserve and International Monetary Fund (IMF) that some funds couldstruggle to meet investor redemptions during a market rout.

Under the proposal, funds would have to maintain a minimumcushion of cash or cash-like investments that can be sold withinthree days. Funds also could charge investors who pull their moneyon days of elevated withdrawals.