Workers from a WA copper mine who have been stood down without pay after a collapse at the site have accused the company of putting profits before safety.

The Birla-Nifty mine, about 350 kilometres east of Port Hedland in the Great Sandy Desert, was shut down about two months ago after a sinkhole formed.

The mine's owner, Aditya Birla Minerals, which is part of a $US40 billion Indian conglomerate, stood down hundreds of workers without pay on the basis it could not be held responsible for the collapse.

It says the incident could not be foreseen and safety is a priority.

But workers disagree, saying the company ignored their concerns, and are pooling their funds to hire a lawyer in the hope of launching a class action against the company.

Brad Gardner worked as the mine's underground foreman for almost two years.

"There was cracking going on in the mine which was not normal," he said.

"The warning signs were there."

Pressure builds as rock is extracted

At Birla-Nifty, copper is extracted from the ground using a method known as stoping.

Holes are drilled into the rock from above and below, before the ore is blasted out.

The extraction process leaves large holes, known as stopes, up to 60 metres high and 25 metres wide.

"The ground is under a huge amount of pressure because we've taken a big hole out of it," Mr Gardner said.

Those holes are filled with a paste made of concrete and waste material from the crushed ore.

The paste acts like a plug, easing the pressure bearing down on the pillars surrounding the hole.

"An engineer would forecast what stopes needed to be mined and what other stopes would be paste-filled, so we could operate safely by filling in one area and mining in the other areas," Mr Gardner said.

But he said the team in charge of backfilling the stopes could not keep up with the amount of ore being taken out.

To make up for a fall in the quality of ore being extracted, the company also ramped up production.

"I was concerned with the ground pressure that was in the mine and it was to do with the regional pillars that hold the whole mine up," Mr Gardner said.

He took his concerns to his immediate supervisor.

"Those pillars should not have had that much stress placed on them and I didn't want to be part of a system where production was going to cost somebody's life," he said.

Concerns 'brushed under the carpet'

Peter Duplessis, who is still employed as a supervisor in Nifty's above-ground workshop, has also raised issues.

"I was notified by my underground fitters that cracks had started to appear in the 17th level workshop - on the floor and in the roof," he said.

"I went down and I had a look at the cracks and it was definitely a big concern to me."

He approached management with those concerns last year.

"They said to us they'll get back to us about these cracks and they never got back to us," Mr Duplessis said.

"It felt to me that they just brushed it under the carpet."

The mine vehicle was covered in mud after a stope cracked.

In February this year, a worker was nearly killed when a stope cracked and a mixture of rock and paste shot out.

He narrowly avoiding being crushed by his vehicle which was thrown into a wall.

The situation came to a head in March when an underground stope collapsed, creating the sinkhole on the surface of the open pit.

The Department of Mines and Petroleum (DMP) shut the site down and workers were flown home.

Those who had annual leave banked were told to use it.

Others got nothing, due to a clause in their enterprise agreement that states the company does not have to pay employees while the mine remains closed if it cannot reasonably be held responsible for the stoppage.

Peter Duplessis said he was convinced Aditya Birla was responsible for the sinkhole and should be paying its workers.

The ABC has obtained a copy of the company's own report into the collapse, which clearly stated the sinkhole was caused by a stope being left open for too long.

The report said the hole then merged with another stope to form one big void, which grew bigger and bigger.

Aditya Birla Minerals managing director Sunil Kulwal said the company's initial report on the sinkhole was not final.

He said it has since appointed independent geotechnical experts to assess the cause.

"They concluded that the most likely cause was a chimney cave-in and the formation of the sinkhole could not reasonably have been foreseen," he said.

"The company can therefore not reasonably be held responsible for the current stoppage."

Worker safety 'a priority' company says

Mr Sunil said safety was a top priority for everyone in the company and has urged workers to be patient.

"From the rock face to the boardroom, every person on our team is accountable and has a duty of care to their safety and the safety of others," he said.

"Right now we are doing everything we can to bring the mine back into operation but we will only do so when we and the DMP are confident it is safe."

The Department of Mines and Petroleum has launched an investigation of its own but it has not yet determined what caused the sinkhole.

Mr Duplessis has not seen a pay cheque in two months.

"Personally I think it is 100 per cent their fault," he said.

"They have to pay us (because) it's not a natural disaster, it's a bad mining method."

The Australian Workers' Union tried unsuccessfully to argue the employees' case at a Fair Work Commission conference last month.

"The indication from the conference was the company can apply the stand-down clause and should we be looking to pursue anything in the future it would actually be quite difficult to do so," the union's Stephen Price said.

The union's problem is there is no proof the company was warned about the specific possibility of a sinkhole forming.

Mr Duplessis and his colleagues hope to raise enough money to approach the Fair Work Commission again.