The U.S. Court of Appeals for the Ninth Circuit in Sullivan v. Oracle Corporation, 547 F.3d 1177 (9th Cir. 2008) applied California's labor code to out-of-state employees working temporarily in California for employers based in the state. The Ninth Circuit later withdrew its opinion and asked the California Supreme Court for guidance. Consequently, the Ninth Circuit decision in Sullivan cannot be relied upon.
In light of the uncertainty surrounding this issue, employers should act cautiously and comply with California law regarding nonresident employees who work within the state.