(Reuters) — A U.S. appeals court on Wednesday dismissed a lawsuit by Edison International employees in California who accused the utility of favoring higher-cost mutual funds over lower-cost ones in its retirement plan, despite a U.S. Supreme Court ruling backing the workers.

The 9th U.S. Circuit Court of Appeals in San Francisco said that while the Supreme Court in May 2015 ruled that federal law imposes an ongoing duty to monitor investments on fiduciaries like Edison, the workers failed to raise that argument in lower courts.

The Supreme Court decision, which revived the Edison case and sent it back to the 9th Circuit, will likely make it easier for 401(k) plan participants to sue their employers for choosing investments that impose excessive fees, especially when those decisions were made years before lawsuits are filed.

But the 9th Circuit on Wednesday said that before reaching the Supreme Court, Edison employees argued merely that changes to their plan triggered a duty to monitor, and not that the obligation was ongoing, so they could not make that claim now.

The case concerned exactly when the role of a retirement plan administrator in monitoring a plan's performance can trigger liability under the federal Employee Retirement Income Security Act, known as ERISA.

The plaintiffs and Edison agreed there was a duty to monitor, but disagreed over what that entailed.

Employees filed suit against Edison subsidiary Southern California Edison Co., which said in a statement that Wednesday's ruling reflected the company's efforts to act in the best interests of 401(k) plan participants.

Lawyers for the plaintiffs did not respond to a request for comment.

The employees argued the company breached its fiduciary duty by, among other things, offering higher-cost mutual funds to plan participants despite the fact that identical lower-cost funds were available.

The main legal issue was whether some of the lawsuit's claims were barred by a six-year statute of limitations under ERISA. The Supreme Court said liability is triggered by the fiduciary's ongoing role monitoring the plan's performance, so the six-year clock routinely resets.

In 2010, a federal judge in California said the claims against Edison were barred. The 9th Circuit agreed in a 2013 decision that the high court last year overturned.