The Securities and Exchange Commission said Tuesday that the activity behind the scandal rocking the $7 trillion mutual fund industry is apparently quite common, with 13 out of 15 brokerages under SEC scrutiny admitting to "revenue sharing" practices.

Revenue sharing occurs when mutual funds pay brokerages to promote the funds’ shares. The SEC’s probe, launched last April, has found that 14 of the 15 firms in question received cash from mutual fund investment advisers and 10 funds accepted brokerage commissions on fund trades as payment, CNN/Money reported.

At a press conference held late Tuesday, the SEC said it is now looking into "dozens of broker-dealers and mutual funds that engaged in this practice to determine whether they adequately informed investors of the conflicts of interest."

"In return for these payments, 13 of the 15 firms appear to have favored the sale of the revenue sharing funds by providing increased access and visibility in the broker-dealer's sales networks," the SEC said.

Nearly half of the brokerages under SEC scrutiny apparently paid brokers more for selling revenue sharing funds or one of the brokerages’ own funds than for selling other funds’ shares, the SEC said at the press conference, adding that half the funds under scrutiny disclosed this activity.

Morgan Stanley agreed in November to pay $50 million to settle charges that it did not tell investors about its compensation agreements with some mutual funds. At that time, the SEC indicated there may be similar arrangements in as many as 15 brokerages.