A number of Manly Fast Ferry deckhands have been stood down indefinitely after returning "non-negative" results in a random drug test.
The NRMA, which owns the ferries, has not confirmed how many workers have been suspended, but a spokesperson said the number was significant enough to affect services between Manly and Barangaroo.
"It's absolutely concerning," he said.
"Our commitment is to safety and we've now got to follow a due process.
"Drug testing is used across our business as part of our zero-tolerance policy towards [drug] use."
Deckhands undertook an initial round of drug and alcohol testing on Monday but it is not yet known which drugs were allegedly in their systems.
The samples were sent for further tests today but the spokesman would not comment on the results until staff had been notified.
It is understood some workers who avoided the initial tests were also stood down.
Staff will learn of the latest test results on Monday.
The spokesman said those suspended were all members of the CFMEU, which had been notified of the incident.
The NRMA took over the ferry service in 2017 and operates 11 vessels through a subsidiary company.
