Metro Train controllers have tested positive for alcohol and cannabis and been subsequently stood down.
The city’s main control centre was tested on Thursday and the three staff in question have been suspended with pay while the operator investigates further.
“Our number one priority is the safety of all of our passengers and staff,” a Metro spokesman said.
“Metro takes a zero-tolerance approach to drugs and alcohol in the workplace — and this policy applies to everyone from our executives to our frontline teams.”
The testing was called after an incident where a train moved unsafely while under maintenance.