The workers were evacuated from the New Jersey Natural Gas administrative offices on Wyckoff Road in Wall Township just after 11 a.m. There are no gas facilities at the site.
About 10 workers were dizzy and nauseous after being exposed to the unknown fumes.
They were taken to the hospital to be checked out.
Six more were being treated at the scene.
Authorities are calling the situation an "air quality issue" in the building.