(Bloomberg) -- The riskiest money-market mutual funds will have to let their share prices fluctuate and charge investors withdrawal fees during times of stress under tougher U.S. rules set for adoption this month.

The Securities and Exchange Commission is poised to impose both requirements on some money-market mutual funds, which required a federal rescue during the 2008 financial crisis, according to a person familiar with the matter who asked to not be named because terms of the final rule haven’t been made public.

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