Fidelity Investments, the Boston financial-services company perhaps best known for its mutual funds, is urging the US Securities and Exchange Commission to refrain from implementing additional rules for the regulation of money market mutual funds.

According to Fidelity, the nation’s largest manager of money market mutual funds, a rule revised in 2010 “significantly reduced the risk” across all types of money market funds and as a result, no further reform is needed at this time. And if the SEC does decide that rule changes are necessary, Fidelity added, then such changes should be “narrowly tailored.”