At least 122 drivers in Ho Chi Minh City have been suspected of using banned drugs over the past two months after transport companies were ordered to inspect their drivers.
The city's Transport Department said more than 700 transport companies which operate bus, taxi and truck services have reported on a total of 29,700 drivers.
Among them, 122 "showed signs of using drugs" while 65 other were not even healthy enough to work as professional drivers.
About half of the 122 suspected drivers are cabbies, with a majority working for two major taxi firms Vinasun and Mai Linh.
Vinasun now has 8,790 drivers and Mai Linh with 4,487 drivers.
Vu Son, a Mai Linh official, said 16 of its drivers might have been using drugs.
The suspected drivers will need to take drug tests and will be dismissed if they cannot pass them.
Drug using has long been reported among professional drivers in Vietnam.
Many people have called for transport companies to disclose the name of drivers who have been found using drugs, arguing that they can still switch to a new company easily.