Johor Immigration Department raided a factory in Senai last night, which has reported to have been hiring illegal foreign workers.
A total of 331 foreigners were rounded up by the authorities for flouting immigration rules.
The raid was led Johor deputy enforcement director Mohd Zariman Mohamad after several weeks of surveillance.
Many of the foreigners, aged between 18 and 40, were found to have entered the country using social visit passes, while some were found without valid travel documents.
The employers is also being investigated for hiring foreign workers without permits.
All those detained have been sent to the Pekan Nanas detention depot for further action.