Hidden, high 401(k) fees that do not decrease commensurately as plan balances rise are individually costing investors hundreds of thousands of dollars over a lifetime of saving, while enriching asset managers with billions.

This is according to a report Hewitt Associates released Monday. Even with increased legislative and legal scrutiny of plan fees over the past few years, Hewitt believes federal action is needed to help plans sponsors and individuals receive better information from investment managers and administrators on these fees.

Such transparency will enable employers to negotiate lower fees and offer competitively priced, best-in-class investments in their 401(k)s.

For a 30-year-old making $50,000 a year, with a plan balance of $50,000 and a typical matching and savings rate, that person would have $115,000 more in savings at retirement if they paid 60 basis points in fees, rather than 90 basis points, Hewitt said.

“Plan fees are eating up thousands of dollars of employees’ retirement savings without them even knowing it,” said Alison Borland, retirement strategy leader at Hewitt. “As concern over employees’ retirement income adequacy levels continues to grow, it’s more important than ever for Congress to enact legislation that will provide employers and employees with an apples-to-apples comparison of the fees in their 401(k) plan. This will enable them to better understand the financial impact of these costs and, if necessary, take steps to reduce them.”