Fly-in fly-out workers who need antidepressants aren't taking them because they fear the drugs will be detected in workplace urine tests and hurt their career, a union says.

After surveying more than 300 FIFO workers, the Australian Manufacturing Workers’ Union said almost 60 per cent of respondents did not seek help for mental health issues because they were worried it might have adverse repercussions on their employment.

AMWU state secretary Steve McCartney said some were so worried they didn’t take medication for mental health conditions.

“Management find out a person is suffering from depression and then usually confidentiality is out the window and the whole team finds out,” one of the respondents said.

Another said workers suffering stress would be fired if they told management about their problem.

“Management openly lie and say they are there to help, and then if you go to them they say `you are not suitable to be in this environment’ and sack them,” another worker told the union.

Mr McCartney said pressure on FIFO workers to stay quiet about mental health issues was going to mount with the slowdown in the resources construction boom.

He said worries about family were the key drivers of stress among FIFO workers.

“Almost 70 per cent of workers said they were worried about family at home, with 65 per cent of them citing poor communications services from site to home as a problem,” he said.

“When we asked them what they would change about the FIFO lifestyle, almost 80 per cent suggested shorter roster lengths, so they could see their families more often, with improvements to communications services on site also suggested.”

The union has submitted its findings to a parliamentary inquiry into the mental health impacts of FIFO arrangements.