Driven to a secluded site lookout by a male Rio Tinto supervisor in his work LandCruiser, Astacia Stevens alleges she was asked to perform a sex act.

WARNING: This story contains explicit content

"He unzipped his pants and leaned back in his seat," she said.

"He was not wearing any underwear and said to me, 'If you want your shirt, you have to get on your knees first'."

Ms Stevens, 33, made the allegation in a submission to a West Australian parliamentary inquiry into sexual harassment in the fly-in fly-out mining industry.

At the time, she was working for a labour-hire company and said the reference to "getting her shirt" meant the supervisor would get her a job with Rio directly.

Allegations of harassment at FMG

Ms Stevens also alleges that while working as a contractor for Macmahon Australia Mining as a haul truck driver on a Fortescue Metals Group (FMG) site, she was propositioned for sex by a Macmahon superintendent.

"I had an incident at the workplace whereby my haul truck nearly hit another haul truck," she said.

"The superintendent at Macmahon that was heading the investigation propositioned me that if I had sex with him, he would make the investigation go away."

Ms Stevens also said she felt so uncomfortable at the gym, that she only used it in the early hours of the morning when no-one else was there.

"I used to have to get up at 3:00am to go to the gym. When I used the gym after my shifts, men employed by Macmahon would always follow me back from the gym to see where I was staying.

"I know this because when I'd leave the gym, men would leave at exactly the same time and I could see them following me.

"I tried to do what I could to avoid men and sexual harassment."

Ms Stevens believes date rape is prevalent 

The submission also alleges Ms Stevens believes other female colleagues were drugged and raped at Rio sites. 

"I am almost certain, but without any proof, that women are being drugged at mine sites and then being raped by men, which the men are passing off as consensual and the women are too scared to report, because nothing is ever done about it but women do discuss these things in confidence with other girls.

The submission also alleges female workers were vilified if they were found to have made complaints about the harassment, and that "a lot" of women did not feel safe to say no to sexual advances. 

"There was always safety presentations and meetings given by Rio Tinto, but there were never any presentations on sexual harassment and the workplace," she said.

"It was almost as if though sexual harassment did not matter to the companies."

CEO condemns alleged harassment 

FMG chief executive Elizabeth Gaines said the allegations of sexual harassment made by Ms Stevens "concern behaviour that is completely unacceptable".

"There is no place for harassment of any kind at Fortescue or in any workplace, and we are taking decisive action to ensure our workplaces remain safe for everyone," she said.

"In line with our zero-tolerance approach to harassment, bullying and intimidation, we will continue to strongly encourage all our team to speak up.

"All complaints are taken seriously and are investigated and handled in accordance with our values."

In a statement, Rio Tinto Iron Ore chief executive Simon Trott said the "behaviour outlined in this submission is shocking and appalling".

"These behaviours have no place at Rio Tinto and will not be tolerated," he said.

"We have launched an investigation into what has been reported, including into how the company responded at the time, and we will take appropriate action based on the outcomes of that review. 

"It's clear from Astacia's submission that we still have a long way to go when it comes to confronting and eliminating serious issues like sexual harassment and sexual assault in the workplace."

Macmahon chief executive officer and managing director, Michael Finnegan, said Ms Stevens' testimony was "deeply disturbing".

"It is also concerning that it appears Ms Stevens did not feel sufficiently confident or empowered to make a formal complaint at the time," Mr Finnegan said in a statement.

"To be clear, Macmahon values all of our people and is committed to providing a safe and positive working environment.

"Sexual harassment and bullying is completely unacceptable."