When you’re a financial services company that offers proprietary mutual funds within your 401(k) plan, expect to get sued.

Current and former participants of the MetLife 401(k) Plan have filed a lawsuit alleging the plan’s fiduciaries violated the Employee Retirement Income Security Act (ERISA)’s duties of loyalty and prudence by using MetLife Index funds in the plan.

According to the lawsuit, MetLife’s action has cost plan participants millions of dollars over the period defined in the lawsuit. The complaint includes charts that show that the MetLife index funds are considerably more expensive than otherwise identical alternatives being used in other large plans. The complaint also alleges that the MetLife index funds were of lower quality than other options when it came to tracking the underlying index.