On April 1, 2026, the Ninth Circuit handed California employers a meaningful win in O’Dell v. Aya Healthcare Services, Inc., No. 25-1528. The court reversed a Southern District of California ruling that had used a procedural doctrine—non-mutual offensive collateral estoppel—to invalidate arbitration agreements for more than 250 opt-in plaintiffs based on two prior arbitrator decisions

California is technically an at-will employment state. But practically speaking, that designation comes with so many asterisks that employers who treat at-will as a blank check to terminate anyone at any time are setting themselves up for costly litigation.

Here are five things every California employer needs to understand about the at-will doctrine:

1. At-Will