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It's common for mutual fund companies to be paid to administer 401(k) plans for employers while also being paid to select and manage investment funds in the plans. It's also a clear conflict of interest—one that typically gets resolved in the fund company's favor, new research shows.

When making plan changes, fund companies add more of their own funds and delete more from outside firms, according to the Center for Retirement Research at Boston College. This bias brings more poorly performing funds onto the menu, researchers found. What’s more, these poorly performing funds tend to remain sub-par. That proves to be a long-term drag on participant returns, since few investors take action to avoid or work around the poor choices they are offered.

Fidelity, Vanguard and most other big fund companies serve in a dual 401(k) capacity by setting the investment menu while also managing funds inside the plan. In all, fund companies manage 56% of the $4.7 trillion in defined contribution plan assets. This is a vast storehouse of Americans’ retirement security—one that, given our savings crisis and public pension ills, must be protected.

A similar conflict of interest between investment advisers and clients is getting a thorough airing this week in Washington. The Department of Labor will hold hearings all week, trying to sort out whether financial advisers working with retirement accounts should be held to the standard of fiduciary, meaning the adviser must put the client’s interests first. The Labor Department believes such a law would keep brokers from putting clients into high-fee retirement savings products. The industry argues it would increase their liability risk and regulatory costs, and discourage brokers from serving small accounts.

The conflict over the dual role of fund companies is not about the fiduciary status of advisers. But the problem persists because employers, who do have a fiduciary role, often fail to take action. That leaves many investors stuck with lousy 401(k) funds, which take a bite out of their retirement accounts. For example, plan administrators remove just 13.7% of their own underperforming funds from the menu every year, the research shows. But they remove 25.5% of underperformers from other fund groups—meaning more of their own poor performers remain. Meanwhile, they are far more likely to add their own sub-par funds compared with choices from another fund company.

The upshot is that 401(k) plan investors must look critically at any changes in their investment options. You can’t blindly accept a substitution on the menu. Look carefully at fees and past performance along with how a fund fits into your portfolio. One good place to start is BrightScope, which can show you the fees and choices of 401(k) plans from comparable companies.

If you find that your plan costs are high—1.5% of assets or more—and your options stink, consider a workaround. You almost always want to contribute enough to get any employer match. But once you have done that, you may find that your spouse has a better plan and you can divert more family savings there. You may find that your company offers a self-directed brokerage option in your 401(k), allowing a more hands-on approach and greater ability to watch fees. You may also be better off contributing additional money to an IRA.

Don’t look for the inherent conflict of a fund company that both manages funds and chooses the funds on your menu to disappear anytime soon. Given the fiduciary discussion in D.C. this week, this issue is nowhere near resolution. As ever, your retirement security is mostly up to you.

Read next: Here's What to Do If Your 401(k) Stinks