The U.S. Supreme Court argued Tuesday over the on-going fiduciary role of retirement plans to monitor investments.

In an hour of give and take in the case of Tibble vs. Edison International, the justices regularly talked about how stringent continuing reviews of existing investments in 401(k) and other retirement plans should be.

They often strayed over the core issue in the case: whether or not a retirement plan can be sued for a violation of fiduciary duty six years or more after a particular investment was purchased. The six-year limit for filing a fiduciary lawsuit is written into the Employee Retirement Income Security Act of 1974 (Erisa).

In the Tibble case, workers at Edison international, a Southern California electric company, have argued that the company 401(k) plan should have invested in the institutional shares of six mutual funds rather than the more expensive retail shares, which had expenses that were 37 percent higher. Two lower courts have ruled that the workers can only sue over three of the funds that were added within the six-year statute of limitations set by Erisa.

During the session, Justice Elena Kagan said retirement plans, like ordinary people, should look at ongoing returns and expenses.

She said the initial purchase by a plan advisor to buy a high expense fund may imprudent, but added it might be prudent not to switch in midstream because of costs.

An attorney for the Edison retirement plan said switching plan investments to meet fiduciary obligations would confuse workers in the retirement vehicles. But Kagan, a former Harvard Law School dean, said participants would like the changes if they brought down fees.

Justice Anthony Kennedy said retirement plans should regularly scour the market for cheaper investment options if that is what a prudent trustee should do.

In questioning the attorney for the plan participants, Justice Antonin Scalia was met with a “no” when he asked, "What’s your position, that every stock that is owned has to be reviewed every year as though it was a new purchase?”

Justice Scalia said the courts are incapable of determining whether retirement plans have done sufficiently careful yearly reviews.

After the hearing, St. Louis attorney Jerome Schlichter, who has helped to bring this and numerous other retirement plan fiduciary cases, said the litigation already has done much to bring down fees for plan participants.

Schlichter said plans should be regularly monitoring funds for fee, performance and management changes and remove investments that have become imprudent.

A ruling in the case is expected by late June.