High number of Sydney train drivers off sick 'coordinated' to disrupt ...

An unusually high number of train drivers and guards called in sick on Friday, in what the government alleges was a "coordinated effort" to disrupt Sydney's rail network, the Fair Work Commission (FWC) has heard.

At least a quarter of services were cancelled on Friday when hundreds of staff failed to show up for work.

The impact was still being felt on Saturday with about 450 delays and cancellations across the network.

About 360 train crew had not turned up to work by 2pm on Saturday, according to Sydney Trains chief executive Matt Longland. 

He said it was due to a "mixture of sick leave and staff who hadn't notified their absence".

At the hearing a Sydney Trains executive said the number of drivers and guards who called in sick was 28 per cent higher than the average over the last six Fridays.

Fatima Abbas, the head of human resources at Sydney Trains, said the uptick led her to believe some of the calls were not genuine.

The NSW government is trying to persuade the tribunal that the mass absences amounted to unprotected industrial action, which is unlawful.

If the FWC is satisfied unprotected action is happening, it must order the activity to stop.

Barrister Jamie Darams SC, acting for Sydney Trains, said the government characterised the "unprecedented increase" in absenteeism as a "coordinated effort".

He said there was no evidence of any virus circulating in Sydney that caused a significant number of guards to call in sick.

Union convenor not reprimanded over text message

Part of the government's evidence of coordination is a text message sent by the  Rail, Tram and Bus Union's (RTBU) Everleigh Convenor, Adam Doyle, on Thursday night.

The text, sent to an unknown number of members, says "[l]et's f--- the network up."

RTBU assistant secretary Paul Dornan said he had short conversation with Mr Doyle over the phone on Friday to "check on his welfare".

"I was worried about his mental health," Mr Dornan said.

During cross examination, Mr Darams asked whether Mr Dornan admonished Mr Doyle.

"No I did not," Mr Dornan replied.

"Are you aware of anyone admonishing him?" Mr Darams said.

"No", Mr Dornan confirmed.

'We don't accept partial work'

Ms Abbas told the tribunal that she instructed that a "471 notice" be issued to employees on February 5.

It informed workers they would not be paid for any work during a shift in which they took part in a partial work ban.

Partial bans described as "go-slows" were set to begin on Wednesday, February 12, but were delayed for 48 hours as the parties tried to seal a deal on pay.

The RBTU's barrister, Leo Saunders, put to Ms Abbas that the notices were an "invitation" for employees to choose between working as normal and staying home.

Ms Abbas agreed Sydney Trains had taken a risk that a "critical number of crew would accept the invitation to stay home".

"Rail agencies must've put plans in place for the risk that a significant number of people wouldn't show up?" Mr Saunders said.

"Yes partly. It's difficult to mitigate that level of absenteeism," Ms Abbas replied.

Mr Dornan told the hearing some drivers were worried they would be docked a day's pay — even if they performed their duties as normal.

"They're worried that if they're late on any part of the journey, that Sydney Trains would dock them, even if they weren't participating in industrial action," Mr Dornan said.

Mr Saunders argued there was "absolutely no evidence" the number of staff off sick was unprecedented.

He said there was some "difficulty" with the government's figures as they contained no information about the normal level of fluctuation.

"How volatile is this data?" he said.

Mr Saunders said there "wasn't a word" from the union about coordinating sick leave.

"It would be the most covert campaign of all time."

Deputy President Thomas Roberts adjourned the hearing to Sunday.