Here's an item that will give more ammunition to the anti Wal-Mart (NYSE: WMT) crowd -- because they really do need more ammunition.

Pensions & Investments reports that Wal-Mart has been sued for allowing participants in its 401(k) plans to be charged "unreasonably expensive" management fees on the mutuals funds available under the plan. The lawsuit is seeking class-action status, and alleges that the company offered participants retail mutual funds rather than lower-cost institutional funds "despite the ready availability of reasonably priced options ... particularly for a massive plan like Wal-Mart's with tremendous potential to leverage economies of scale."

If you're wondering about how you should invest your own money, here's a hint: the lawyers for the plaintiff compared Wal-Mart's high-cost managed funds to the ultra-low cost funds offered by Vanguard. For example, the actively managed retail fund available to Wal-Mart investors has an expense ratio 1.59% vs. 0.55% for a comparable fund. Over time and many billions of dollars, that adds up: The suit is seeking to recoup at least $60 million in allegedly excessive fees.

Virtually all intelligent and unbiased personal finance experts suggest that retirement money be invested in ultra-low cost index mutual funds. If a lawsuit is what it takes to make Wal-Mart off that option to its employees, than so be it.