Here’s an example of just how costly it can be when workers decide you’re not doing everything in your power to avoid paying excessive 401(k) fees.

Wal-Mart Stores and Merrill Lynch (the company’s retirement plan provider) just agreed to settle a class-action lawsuit for $13.5 million. The suit claimed the world’s largest private employer didn’t do enough to negotiate lower 401(k) fees.

The lawsuit dates back to 2008, when a Missouri Wal-Mart worker accused the company – known for using size to get the lowest possible prices from its suppliers – of failing to negotiate lower fees for the mutual funds in its 401(k) plan. According to the suit, Wal-Mart offered just 10 investment options, most of which carried “retail” – a.k.a, high – fees.

While the company admitted no wrongdoing, the majority of its settlement will go toward reducing future 401(k) fees.

Merrill Lynch wasn’t initially named in the suit. However, during the trial, the firm was charged with receiving kickbacks from mutual fund companies in exchange for allowing them to be in the plan.

Tags: Class action lawsuit, Excessive 401(k) fee lawsuit, Merrill Lynch, Settlement, Wal-Mart Stores