The Securities and Exchange Commission and class-action lawyers are targeting stockbrokers who did not tell investors when one class of mutual funds — "A" shares vs. "B" shares — represented a better deal.

Attorneys general in New York and Massachusetts have taken aim at sales incentives designed to get brokers to push certain funds.

Meanwhile, the House Committee on Financial Services is writing a bill that would require fund companies to shed more light on what investors pay in the way of fees — and who shares in the pie.

Pennies in fees become billions in industry revenue after being applied to the $6.4 trillion held in mutual funds last year — more than $70 billion in fees, by Bogle's reckoning.

Mutual-fund companies "have arrived at the point where we just have to be more open," said the founder of Malvern, Pa.-based Vanguard Group.

Investors must focus on costs, said Russell Kinnel, director of fund analysis for Morningstar, the fund-ranking firm in Chicago. Fees could spell the difference between meeting investment goals and missing them.

"We may well be in a low-yield era," Kinnel said. "Yet fees have gone up. You could wind up giving back a quarter or a third of your returns."

Call it the dark side of compound interest. An investment of $10,000, earning 8 percent a year for 25 years in a mutual fund with operating expenses of 0.5 percentage points and no sales commission, or load, would grow to $60,419.

A similar investment, after subtracting a 5.5 percent load and expenses of 2 percentage points, would amount to $39,055, or 35 percent less.

For comparison purposes, mutual-fund firms publish expense ratios: Investment management fees and operating expenses are expressed as a percentage of a fund's assets.

But expense ratios do not cover everything. By Bogle's calculation, the average expense ratio of 1.3 percent would double if the fund disclosed sales commissions on an annualized basis, plus their securities trading costs.

Under House Resolution 2420, funds would be required to provide each investor with an estimate of his or her share of fund expenses, along with an estimate of how much funds pay to buy and sell securities they hold on behalf of fund investors.

The bill would require brokerage firms to tell funds' boards of directors about "soft-dollar" deals: inducements such as free research given by brokerage firms to fund managers to land them as clients.

The mutual-fund industry opposes some of the disclosures as complicated and expensive.

"The real question in any of this is 'Would it hurt or help investors?'" said Matthew P. Fink, president of the Investment Company Institute, an industry trade group.

In recent enforcement action, the SEC alleged that Prudential Securities brokers did not tell prospective clients that they would receive discounts if they invested $50,000 or more in regular class A shares, in which commissions were taken up-front.

Reluctant to cut their own fees, according to the SEC, some Prudential brokers steered clients to a share class that was not discounted.

In B shares, the salesperson collects the commission from the fund rather than from the investor. The fund charges higher fees to recover the money, and levies a deferred charge if the investor leaves too early, typically within five years.

"The whole reason B shares exist is to obscure the commission you're paying," said Morningstar's Kinnel.

C shares also bear an indirect sales charge that is recovered in the form of higher fees.