The deaths, possibly caused by an industrial accident, happened at the airport Monday morning.
Cal/OSHA says the incident is under investigation.
The names of the two employees who died have not been released.
UPS released a statement: "We're deeply saddened and express our condolences to the families and associates of the victims. We are cooperating with the authorities in their investigation. We are unable to release the names of the individuals involved pending confirmation of notification of relatives."