Fidelity Investments said on Tuesday the U.S. Securities and Exchange Commission's push to change the long-held pricing convention of money market funds grossly underestimates the scope of the reform.

Boston-based Fidelity, the largest money market fund provider in the world, said the pricing reform put forth by the SEC would affect about 65 percent of money fund assets.

"The (SEC) staff estimated that only 30 percent of all (money market fund) assets would be subject to a floating (net asset value) if adopted by the SEC," Fidelity said in a comment letter. "The SEC grossly underestimated the industry assets that would be impacted, which we estimate to be closer to 65 percent of all (money market fund) assets."