Two other non-Vanguard funds were offered, as well as an Anthem stock fund.

Each fund in the lineup charged fees “far in excess” of what Anthem could have obtained, given the size of the plan, according to the complaint, which was filed in U.S. District Court for the Southern District of Indiana. Anthem is headquartered in Indianapolis.

“Jumbo retirement plans, such as the (Anthem) Plan, have much more bargaining power to negotiate low fees for investment management services than even large plans,” write attorneys for the plaintiffs, who are being represented by St. Louis-based Schlichter, Bogard and Denton.

While the Vanguard funds offered had low expense ratios, the plaintiffs are claiming there were better options available.

For instance, up until July 22, 2013, the plan offered the Vanguard Total Bond Market Index Fund, costing participants 20 basis points. That intermediate-term bond fund is available to retail investors with a minimum of $3,000 investment, according to Vanguard’s website.

The institutional class share of the same fund is available for 5 basis points, but requires a minimum investment of $100 million, Vanguard’s website says. The complaint shows that participants had more than $422 million invested in a Vanguard intermediate bond fund at the end of 2014.

The Vanguard Extended Market Index Fund, an aggressively structured domestic stock fund, was offered for 24 basis points, while the institutional share class was available for 6 basis points, so long as a minimum of $100 million in assets were invested.

In one case, the spread between the retail and institutional expense ratios was as little as 2 basis points.

In 2013, Anthem restructured its investment menu, switching in institutional shares of funds and moving Vanguard’s TDF series to cheaper collective trusts.

That action served to fuel the plaintiffs’ claim.

“The lower-cost share classes of the identical mutual funds were available to the plan many years before Anthem restructured the investment lineup in 2013,” the claim says. Several were available as early as the late 1990s.

The lineup’s two most expensive options—the Artisan Midcap Value Fund and the Touchstone Sands Capital Select Growth Fund—cost participants 120 and 103 basis points, respectively, and each held more than $130 million in assets.

Those are not Vanguard funds, but the complaint says trustees could have saved participants “millions” by using cheaper Vanguard options.

Anthem also failed to monitor the recordkeeping fees Vanguard charged, according to the complaint.

Given the size of the plan, a reasonable per-participant recordkeeping fee would have been $30 per participant, argue the plaintiffs.

But between hard-dollar fees and revenue sharing agreements, in some cases from its own funds, Vanguard was earning as much as $80 to $94 per participant in recordkeeping fees until September 2013, when Anthem initiated a flat $42 recordkeeping fee.