Lawyer Rory Markham of Canberra specialist class action law firm Adero Law was at Beresfield Bowling Club on Tuesday with injured former Mount Arthur mineworker Simon Turner and another dozen or so contract mineworkers from Mount Arthur and other mines in the region.

Mr Markham acknowledged that his firm was challenging a situation that everybody else in the coal industry – including various regulators and the mineworkers’ union – accepted as lawful.

But he said his firm had viewed the situation as an outsider looking in, and convinced a hard-nosed litigation funder, Augusta Ventures, to put up the millions of dollars needed to run the case.

“In order to satisfy both the investors (Augusta Ventures) and to make sure of our legal obligations, we have completed over six months of due diligence, both of the legal arguments and probably the most thorough analysis of underpayment ever undertaken in the Hunter Valley,” Mr Markham said.

He said the figure of $40 million to $50 million had been calculated by looking at the money Adero believed was owed to up to 1500 mineworkers it said had worked at Mount Arthur as “casuals” over the past six years.

“This is not a claim we have come to lightly,” Mr Markham said.

As the Newcastle Herald has reported, Adero’s interest was sparked by an approach from former Mount Arthur “casual” mineworker Simon Turner, who was injured when an excavator shovel hit the cabin of his truck in December 2015.

Related: One accident changed his life forever (July 25, 2016)

Mr Markham said Mr Turner was a “courageous” individual who had campaigned steadfastly to uncover what Adero came to agree was a series of harmful and unfair situations in an industry that had come to rely so heavily on casual labour that it was creating “perverse” outcomes.

Mr Markham said the term “casual was meant to allow for flexible and infrequent engagement” on the job.

But it had come to a point where Mount Arthur and other mines had significant portions of their workforces employed by labour hire companies and defined as “casuals” despite having their rosters set for months in advance at a time, and having to apply in advance for leave as any full-time or part-time worker would.

Mr Markham said working under the same conditions as permanent workers without the entitlements made a mockery of the term “casual engagement”.  

Despite Mr Markham saying that some documents had been lodged with the Federal Court on Monday and that others were being lodged on Tuesday, mining giant BHP disputed this, saying that as far as it could tell, no documents had been filed in relation to the Adero class action.

Related: Deeper reading on the Adero Law class action (June 25, 2018)

A BHP spokesperson said the situation remained the same as it was in February, when the Herald first reported the likelihood of the case. The spokesperson said that despite the passage of four months, there had still been no formal correspondence from Adero.

Mr Markham disputed the BHP position, insisting that there had been correspondence between Adero and the respondents to the case, or their lawyers.

Describing the action on Tuesday, Mr Markham described the case as a “closed class action” with injured former Mount Arthur casual Simon Turner as the “lead representative”.

Once all the documents were filed it would become an “open action” covering anyone who worked as a casual at Mount Arthur in the past six years: these people would be given the right to “opt out” of the case should they wish.

Mr Markham said the first action would be served against labour hire firm Chandler Macleod and against the BHP companies that owned the Mount Arthur mine.

He said the case would be listed for “case management” where a defence would have to be filed by the companies as to why Mr Turner was not entitled to accident pay and why he was “said to be a casual when he was engaged on the same roster as their permanents”.

He said this should take about 28 days, after which Adero would “push very heavily for discovery”, looking for evidence about what BHP and Chandlers “knew about the way they engaged their workforce”. 

He said Adero would be “working very heavily on getting a mediation” and a successful outcome in the court.