As reported on Friday, the Canberra law firm has been working with an injured former Mount Arthur mineworker, Simon Turner, and intends lodging a class action in the Federal Court over the use of casual labour at the BHP mine. Labour hire firms Chandler Macleod and Tesa are also named.

Mining sources downplayed the importance of the case, saying the firm was simply seeking free publicity with its claims.

Despite this, neither BHP nor the Minerals Council of NSW was prepared to comment on the validity of the law firm’s main claim – that enterprise agreements using casual employment are illegal because they conflict with the award, which recognises only full-time and part-time (but not casual) employment.

Chamberlains partner Rory Markham said the firm had done three months of due diligence and had opinions from leading senior counsel and a London-based investment committee.

BHP and Chandler both denied knowing of the claim before publication of Friday’s article and Tesa’s owner, Programmed Maintenance Services, said it was not aware of any “legal or non-compliance employment matters” relating to contracts at Mount Arthur that ended in 2014. It would “review” any arrangements where non-compliance was claimed.

CFMEU district president Peter Jordan said the union had members working for Chandler and Tesa, and was looking after their interests. He said the people raising issues at Mount Arthur were not union members.

He added that the union had last year won two Federal Court cases against labour hire firms Workpac and OneKey, but both cases were now the subject of appeal.

Mr Markham said these Queensland cases represented “only about 10 per cent of the matters we wish to represent these workers on”.

“We would appreciate it if the CFMEU would assist in protecting these vulnerable workers,” Mr Markham said.

“Our door is always open.”