Although mining unions have opposed casual and contract workers from the start, companies, aided by labour market deregulation, have been able to introduce them in substantial numbers.

In recent years, some mines have had their entire workforce employed by a contractor: a typical example is Peabody’s Wilpinjong mine near Mudgee, which was operated on contract by Thiess from 2007 to 2013.

Other companies, including BHP Billiton at Mount Arthur, took a different approach, and used a mixture of direct BHP employees and contractors, depending on labour requirements at the pit.

As the Newcastle Herald has reported this week, BHP uses a national labour hire company, Chandler Macleod, to provide contract labour at Mount Arthur. The company this week declined to say how many contractors were on site, arguing the numbers varied from time to time but there were at least 273 when Chandler signed an enterprise agreement last year with the Construction, Forestry, Mining and Energy Union. Their numbers are understood to be higher now.

BHP says it has no control over Chandler’s employment conditions.

Chandler Macleod says these conditions are set out in a document known as the Chandler Macleod Northern Districts of NSW Enterprise Agreement 2015, which it says was “validly approved” by the Fair Work Commission on June 4 last year.

In the decision approving the agreement, Fair Work Commission says it is satisfied that the three relevant sections of the Fair Work Act: sections 186, 187 and 188.

Although these sections are detailed, they can be summarised as saying that the employees have to genuinely agree – rather than be “coerced or threatened to be coerce(d)” – to the conditions, which must pass the “better off overall” or BOOT test.

Barrister and Greens MLC David Shoebridge, who has followed the Mount Arthur issue closely, points out that the enterprise agreement appears to be inconsistent with the Black Coal Mining Industry Award 2010, which governs the basic employment standards in the industry.

Mr Shoebridge says the award only allows for two types of employment as far as mine workers are concerned: they are either full-time or part-time. Casual employment is in the award, but only for staff employees.

And however the jobs of the Chandler Macleod mine workers are described, they are certainly not staff.

Injured Mount Arthur mine worker Simon Turner – who as the Herald has reported this week worked at the mine with Chandler until he was injured in December – says the union’s acceptance of casual employment at Mount Arthur, despite it being in apparent conflict with the award – was one of the reasons that he and other Chandler workers were angered with the CFMEU for supporting the enterprise agreement.

In a letter to the Fair Work Commission last year, Chandler said it had “zero” casual employees at Mount Arthur, whereas in numerous documents – including information for employees on its own website – it clearly states the Mount Arthur workforce is casual.

In a letter its members at Mount Arthur in April last year, the CFMEU said Chandler Macleod had “informed us that all of their labour hire employees are employed casually under the terms of the Black Coal Industry Mining Award and as a result are not receiving annual leave, sick leave or other entitlements that should be afforded to permanent employees”.

“We have brought to Chandler Macleod’s attention that there is no casual production classification in the award,” the letter said. “The casual classifications are only for staff positions.

“Don’t be fooled into thinking that the agreement . . . is for your protection, in fact it is to aid them to get around providing terms and conditions that should be afforded to you under the award.”

Discussing this on Wednesday, Mr Jordan said the union had agreed not to pursue a prosecution against Chandler for “engaging employees unlawfully” provided they back-paid their workers $3 an hour. He said Chandler had originally employed its Mount Arthur workers under a “couple of pages of common law agreement”.

When some of its employees joined the CFMEU, the union pushed the company to obey the law.

“Chandler had two choices – either make them permanent, with the relevant entitlements, or strike an enterprise agreement that passes the relevant tests, including the BOOT,” Mr Jordan said.

Mr Jordan said a coal mining enterprise agreement could include casual employment, but Mr Turner said his legal team was adamant it was not a condition that could varied from the award.

Asked how the Chandler agreement could pay so much less than BHP at Mount Arthur and still pass the relevant tests, Mr Jordan said a major reason was that the Chandler workers did not receive the production bonus paid to BHP employees.

Mr Turner said some BHP mine workers made “a great play” of asking their colleagues over the two-way radio “how much the bonus was for the week, knowing that we weren’t getting it”.

Mr Jordan says the Fair Work tests need toughening up.

“The bargaining and agreement making provisions of the Fair Work Act are both weak and farcical.”