The court's opinion stemmed from lawsuits brought by cashiers at the CVS drugstore chain and tellers at Chase Bank who said they were wrongly denied a place to sit while working. Experts called the opinion a victory for the cashiers and tellers.

"When all is said and done, the burden of proof is going to be on employers in most situations to determine why a seat would not be reasonable," said Stephen Hirschfeld, a San Francisco-based labor lawyer who advises companies.

Companies likely will err on the side of providing a seat after Monday's opinion, and those facing similar lawsuits will settle, Hirschfeld said.

The ruling is aimed at clarifying state labor regulations that require employers in California to provide workers with "suitable seats" when the nature of their work reasonably permits the use of seats.