The U.S. Supreme Court is taking a close look at a question individual investors have long asked about their mutual funds, but the courts have largely ignored: Why am I getting charged twice as much as big institutional clients?

Sure enough, the money-management services that different classes of fund clients get aren't the same. Institutions like pension funds and foundations may not need toll-free customer hotlines. They don't require as many of the prospectuses and other fund reports that individuals often throw away, even though they're printed and mailed at great expense. Individuals move relatively paltry sums in and out of a fund, piling up higher transaction costs than big clients.

Still, the investments a fund makes are often the same for both groups, and the returns similar — though individuals' higher fees take a bigger bite from their results, regardless of whether markets are up or down.

So it can be galling for an individual to pay an expense ratio of, say, 1 percent of cash invested as an annual fee, versus 0.5 percent for an institutional client enjoying what is in effect a bulk rate.

Courts have been reluctant to consider such disparities, and have rarely sided with investors. Instead, the comparisons that courts have allowed focus on whether a fund's fees are so far out of line from what similar competing funds charge as to be unreasonable.