The mandatory drug test was ordered after the mayor received complaints about abusive drivers and crews during garbage collection operations.
Resident claimed that the abnormal behavior of some garbage truck drivers is due to illegal drug use.
Fredirika Rentoy, chief of the Environment Protection and Waste Management Division (EPWD) at City Hall, reported that 31 out of the more than 1,000 drivers and helpers failed in a recent drug test.
She said those who tested positive are now undergoing confirmatory tests.
Those found to be drug users would be blacklisted.
The city government employs the services of five garbage contractors and several special operation contractors. Perseus Echeminada