A class action representing hundreds of Hunter Valley coal workers will examine what it means to be a casual employee in Australia.

The BHP-owned Mount Arthur coal mine at Muswellbrook is the largest coal mine in New South Wales with a production workforce of about 1,900 people, including direct employees and labour hire contractors.

The law firm leading the class action, Canberra-based Adero Law, said it would be run on behalf of about 400 casual workers.

The law firm alleges BHP has taken advantage of contract labour-hire companies Chandler Macleod and Tesa, which engage workers as casual rather than permanent employees.

Stability 'destroyed'

Former coal miner Simon Turner is the lead claimant.

He has not worked since a workplace injury in 2015 left him with a total and permanent disability.

The 47-year-old suffered spinal injuries after the truck he was operating at the Mount Arthur coal mine was hit by a coal excavator.

But he claims he was refused the industry standard accident compensation because he was classified as a casual worker.

He said he had worked the same role as a permanent employee for more than a year, but now had been left with nothing.

"It's very hard because you've got the same qualifications and work the same roster and you get paid less," Mr Turner said.

"You don't have any job security, you don't have any time to spend with family to take holidays, you go to work sick.

"Your whole family life and stability is basically destroyed and taken away from you."

Mr Turner speaks to the media near Newcastle at the launch of a class action over the casualisation of the mining workforce. ( ABC News: Annabelle Regan )

Adero Law principal Rory Markham said the class action would allege that BHP was involved with Chandler Mcleod and Tesa over a period of six years to casualise its workforce.

He hoped the class action would change the casualisation of the Australia mining workforce.

"When you expect someone to show up for 18 months on the same roster, when you expect them to ask for leave in advance, an industry where you have to put in a leave certificate but told you're engaged hour to hour, you are making a mockery of a casual engagement and you're really calling it a simple sham," Mr Markham said.

Current casuals join action

Grahame Beech is a casual worker at the Mount Arthur coal mine. ( ABC News: Lauren Kempe )

It is not just former casual workers who are taking part in the class action.

Grahame Beech is a current casual operator at the Mount Arthur coal mine and was recruited through Tesa.

He has been a casual employee for six years.

"No one should stay casual for six years in any job," he said.

Mr Beech said there was a clear distinction at the worksite between casual and permanent employees.

"We're just called 'connies' [contractors]. There definitely is a culture difference."

Mr Turner said casuals were always hopeful they would be offered a permanent job.

"That's the magical carrot that's dangled in front of everyone," he said.

"Turn up to all your shifts, don't have any time off, take all your breaks, do your work … you might have a permanent job someday."

Claims valued at more than $40 million

Mr Markham said the class action was closed with about 400 people signing on.

However, when it is officially filed and served it will be deemed an open action that will cover all workers that fall within the class definition.

"The claims themselves are in the value of in excess of $40 million," he said.

"We believe it's covering between 800 and 1,500 individuals that were engaged as casual at the Mount Arthur site in the period of the last six years."

Adero Law said it was investigating further action against other mining companies.

BHP said it had not received any formal communications about the claims being made.

Chandler Macleod said it had not been notified of any action against it, and in the event of any action it would respond to the court process.

Another labour hire company, Programmed, which acquired Tesa, has been contacted for comment.