WASHINGTON — Millions of workers who contribute to 401(k)-style retirement plans are unwittingly losing money because fees charged to manage their funds are difficult to uncover, according to a government report.

A report released Thursday by the Government Accountability Office recommends that Congress enact legislation requiring employers to provide an easy comparison of these fees both for workers and the Labor Department that oversees the plans.

The incoming Democratic chairman of the House Education and the Workforce Committee said he will call hearings on this issue early next year.

"It's critical that workers' hard-earned savings not be wasted on excessive fees," Rep. George Miller, D-Calif., said.

For example, an investment of $20,000 with an annual return of 6.5 percent would grow to $70,500 over 20 years with a 0.5 percent fee. But if a fee of 1.5 percent is charged instead, the net retirement savings is reduced to $58,400, according to an example used by the GAO.

Current regulations don't require employers to make it easy for workers to find out these differences, although 92 percent of 401(k) plan participants are allowed to choose their own investment options.

"In order to get a complete picture of fees, participants must collect various documents over time and may be required to seek out some documents," the GAO report found. "Furthermore, the documents that participants receive do not provide a simple way for participants to compare fees — along with the risk and historical performance — among investment options in their 401(k) plan."

Moreover, some investment options — such as annuities — are not required under current law to disclose their fees, making comparisons impossible.

The Labor Department does have the authority to oversee these fees "but lacks the information it needs to provide effective oversight," said the report. "Labor officials told us that it is difficult to discern whether a fee is reasonable or not on its face, and therefore, investigators rarely initiate an investigation into a fee's reasonableness."

The Labor Department said it is planning to finalize new rules in this area next spring.

Investment fees represent most of the cost of operating a 401(k)-style plan, while only a small fraction involves employers record-keeping expenses.