Weighing in on a dispute brought by employees of Rosemead utility Edison International, the Supreme Court unanimously ruled Monday that retirement plans have to monitor the investment options they offer, a move that could make it easier for employees to file lawsuits in the future over funds that charge high fees.

At issue are three retirement funds offered by Edison, parent of Southern California Edison, that were more expensive than some identical – and lower-priced – mutual funds that could have been offered, according to the lawsuit filed by Glenn Tibble and other Edison employees.

The employees alleged Edison International had breached its fiduciary duty by not offering the lower-priced plans. The 9th Circuit Court of Appeals had rejected employees’ claims because they were filed after a six-year statute of limitations had expired. But the Supreme Court on Monday sent the case back to the 9th Circuit, ruling that a prudent trustee must monitor investments on an ongoing basis and that a statute of limitations should not apply.

That court will now decide whether the three mutual funds should have been removed from Edison’s plan offerings sooner.

Edison International spokeswoman Lauren Bartlett said Monday’s decision does not question the company’s loyalty to those in the plan and that Edison is committed to offering a variety of investment options for its employees.