Nichols Kaster compared the Fujitsu plan’s fees with those of about 650 other plans with more than $1 billion in assets. Among 401(k)s with that much money, the average plan has annual costs that amount to 0.33 percent of assets, according to the complaint; it estimates that Fujitsu’s costs were 0.88 and 0.90 percent for 2013 and 2014.

That would have led to at least $7 million in excess fees that could have been socked away in employee nest eggs, the complaint stated. Fujitsu America, which provides technology and business support to affiliated companies, has yet to answer the complaint or make an appearance in the case, and a company spokesman declined to comment.

Lawsuits such as this one are just the beginning, said Marcia Wagner, a principal at the Wagner Law Group who represents plan sponsors and vendors under the Employment Retirement Income Security Act. The case follows a parade of high-profile suits filed by Jerome Schlichter, of the St. Louis law firm Schlichter Bogard & Denton, alleging breaches of fiduciary duty at some of the largest plans in the U.S.

The mega-settlements Schlichter has won, along with a U.S. Supreme Court ruling last year that put plan fiduciaries on high(er) alert about the need to continuously monitor plan investments, has encouraged more law firms to develop and expand their fiduciary litigation practices.

“It started with Schlichter doing cases against very large corporations in America," Wagner said. "And now it's going to start to be a free-for-all.”

The focus of the suits is expanding as well, with a wider array of plan permutations and fees coming under scrutiny. "The pace of cases being filed has quickened, and the areas of challenge have broadened," said Richard McHugh, a lawyer and vice president of Washington affairs for the Plan Sponsor Council of America, which represents defined contribution plans.

Related: 7 ways plan fiduciaries should monitor target-date funds

Additionally, he thinks the U.S. Department of Labor's new fiduciary rule will widen the number of defendants who are named in these lawsuits.

With more attorneys seeing an opportunity, smaller plans are starting to feel the heat. After launching four 401(k) lawsuits alleging breach of fiduciary duty late last year, Minneapolis-based Nichols Kaster has filed four more in 2016, most recently against Fujitsu and American Century's $600 million plan. This year has even seen a 401(k) plan with less than $10 million in assets get hit with a lawsuit, a development that garnered the attention of many players in the small plan universe.

The complaint against Fujitsu alleges that the plan's participants were made to pay high fees for its choice of imprudent investments—imprudent, in some cases, because the plan failed to use the cheapest share class for many mutual funds. In one instance, it allegedly used a class with an expense ratio that was 43 basis points higher than another it could have used.

The complaint also highlighted what it deemed "idiosyncratic" investments in custom target-date funds created by Boston-based investment advisory firm Shepherd Kaplan LLC, which is also a defendant in the lawsuit. The firm, which became the plan's investment adviser in late 2011, was a “named investment fiduciary” until July 31, 2015. Shepherd Kaplan General Counsel Bruce Goodman said the complaint is without merit.

Target-date funds automatically rebalance portfolio holdings among asset classes as savers get closer to their retirement date. The custom target-date funds allocated “a wildly excessive percentage of assets to speculative asset classes such as natural resources, emerging market stocks, emerging market bonds, and real estate limited partnerships,” the complaint against Fujitsu stated.

A number of the funds used by the plan allegedly had track records shorter than three years and were “extremely expensive.” As of Nov. 30, 75 percent of the target-date funds had underperformed their benchmarks, the plaintiff employees claimed.

An unusual wrinkle in the case is the large role that one fund, the Shariah-compliant Amana Growth Fund, played in the plan. At the end of 2014, Fujitsu's plan held over $225 million in Amana Growth, which was used in the plan's target-date (also called lifecycle) funds as a large-cap growth offering.

Yet the plan still used the share class available to retail investors, with fees of 1.10 percent, rather than the institutional share class that became available in 2013, which had a fee of 0.87 percent. In 2014, that decision led to more than $500,000 in excess fees, the lawyers claimed.

Related: Target-date fund participants least likely to react in down markets

Part of the issue with Fujitsu's use of the Amana fund is that its performance history might not be due to strong management but instead to the fund’s unique dictates. It can't invest in financial stocks or very leveraged firms because of a prohibition on paying or receiving interest, said Carl Engstrom, a lawyer with Nichols Kaster.

The fund also stays away from energy and real estate stocks. Those caveats mean it doesn't closely track large-cap growth benchmarks, so it could be problematic in an asset allocation fund that's designed to track benchmarks. “So they smell like a rose from 2007 to 2008 because it looks like they intelligently avoided financial stocks when its not indicative of that—their hands were tied,” said Engstrom.

The complaint also highlights a practice that many 401(k) plan participants may not know exists: “revenue sharing” between the company offering the funds and the plan's sponsor — the employer. It's an allowable practice, though it's become more controversial in recent years. As the complaint describes, in some cases it can mean that employers benefit from keeping high-cost investments in the plan because they allow for "revenue sharing" to subsidize the plan’s administrative costs.

Nichols Kaster alleges that was the motivation of the Fujitsu plan, and that because of this practice, it paid about $3 million in excess record-keeping fees in 2011. In a regulatory filing for the Fujitsu Group Defined Contribution and 401(k) Plan, the plan's administrator noted that a major service provider received indirect compensation. "Substantially all expenses incurred for administering the plan are paid by the plan," according to the filing. "Certain fees applicable to the investment options are netted from the returns of those investments."

The 401(k) improved its offerings at the start of 2016, the law firm noted. It moved some investment options into the least-costly share classes, and in March again changed the plan’s management and investment lineup, hiring a new adviser as fiduciary and replacing all the “Fujitsu LifeCycle” funds with a new set of customer target-date funds called the “Fujitsu Diversified” funds (it also replaced most of the funds in the plan).

"Unfortunately for the plan and its participants," lawyers for the employees wrote in the complaint, by moving to cheaper share classes Fujitsu "did not refund the millions of dollars in excessive fees that participants needlessly paid due to defendants' failure to make this change years earlier."

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