The workers with SEIU-USWW are in the midst of contract talks and are rallying in support of a proposed hike to minimum salaries.
The workers began blocking traffic just before 11 a.m., and vehicles were being redirected to the arrivals area and the departure drop-off areas at other terminals.
An airport spokesperson said people should consider using the "Kiss & Fly" area located at the Rental Car Center for International Terminal pickup and drop-off while the rally continues.
MORE: From worker strikes to activism, multiple May Day protests held throughout the Bay Area
Domestic terminals are unaffected.
No time estimate was given for when the roadway would fully reopen to traffic, but cars were being allowed to use one lane by about noon.
The rally involves passenger service workers, including baggage handlers, wheelchair agents, aircraft cleaning staff and catering crews, among others.
Stay with ABC7 News for the latest details on this developing story.