DES MOINES, Iowa – Workers protesting fees paid out of their 401(k) accounts want to know what the money is used for and who gets it and want proof that the charges are justified. And they’re going to court to get the answers.

Such lawsuits heat up whenever there’s a major stock market downturn, said Fred Reish, a Los Angeles attorney who specializes in employee benefits law.

“You can almost take a look at the stock market, note when the bottom has hit, and put a pencil mark on your calendar. One year later will be the beginning of the litigation,” he said. “It’s almost like clockwork.”

The number of cases against large companies including Kraft Foods Inc. and Wal-Mart Stores Inc. has accelerated, and now mid-sized and smaller companies are becoming targets.

The fear of lawsuits has been enough to push companies offering 401(k) plans to improve oversight of fees and work harder to lower them.

The average 401(k) plan pays about 1.5 percent of assets annually in fees, says the Center for Retirement Research at Boston College. Generally speaking, fees for more than a half dozen services may be charged, including recordkeeping, administration, brokerage and investment management. In addition, several other indirect fees and expenses could be charged, said Marcia Wagner, a Boston attorney specializing in employee benefits.

The fees are significant because a 1 percentage point difference in fees would reduce overall retirement income by 28 percent over a lifetime of saving, according to the Department of Labor.

In 2001, a group of small companies with 401(k) plans sued Nationwide Insurance and its financial services business, which provided their plans. They accused Nationwide of making deals with mutual funds offered in its plans to share some of the investment revenue.

The lawsuit claimed the deal violated the Employee Retirement Income Security Act, which dictates how employers and plan providers must behave when overseeing worker retirement funds.

Nine years later, the case continues to drag on in the courts, but a Connecticut federal court judge’s initial ruling in favor of the plaintiffs opened the door to this new area of litigation targeting retirement fund fees and who had fiduciary responsibilities.

In 2006, a new series of lawsuits began showing up on federal court dockets in which workers accused employers, mostly large companies, of allowing excessive fees.

Since then, dozens of cases have been filed. They tend to cost companies hundreds of thousands of dollars –if not millions – to defend against.

The U.S. Department of Labor announced last month that starting next July, any service provider paid more than $1,000 in connection with a retirement account plan must provide detailed fee reports to investors.

That includes brokerage services, recordkeeping companies and major providers and administrators of 401(k) plans including Fidelity Investments, The Vanguard Group, Principal Financial Group and Charles Schwab Corp.

A second Labor Department regulation will be released in a few months that requires employers to provide workers with details about the fees charged for the choices they make in their retirement account.