Senator Roberts attacked the union, the minerals council and various federal agencies involved in the coal industry during three Senate estimate committee hearings in Parliament House on Wednesday afternoon and evening.

The chief executive of the NSW Minerals Council, Stephen Galilee, said the council would "examine the issues ... raised including the concerns about complaints mechanisms, to assess any implications for our member companies".

READ MORE: Senator Malcolm Roberts alleges 'deceitful' mistreatment of 'casual' coal miners

On Thursday morning, Senator Roberts issued a statement saying the documentary evidence and the work histories of mine workers he had spoken to in the lead up to the hearing revealed an organised strategy to "deliberately under pay, exploit and defraud workers of their entitlements".

"This deliberate exploitation of hundreds of coal miners, with the full knowledge of the union, employers and state ministers, is astonishing," Senator Roberts said.

"The dishonesty is both audacious and callous, and has caused serious emotional distress for the miners.

"Additionally, miners tell us that employers have not reported injuries to authorities and miners have been told to not report workplace accidents and threatened with the sack in a toxic and unsafe culture, with accident pay below the award rates.

"This is criminal."

In his statement, Senator Roberts thanked Stuart Bonds - a mine worker and CFMMEU member and One Nation candidate who challenged Joel Fitzgibbon at the May federal election - for bringing the issues to his attention.

Mr Bonds told the Herald that he could not initially believe the complaints he was receiving from fellow mine workers, but they had been thoroughly researched and validated.

"These people have been to both major political parties, and both parties couldn't or wouldn't do anything, so they came to us," Mr Bonds said.

Responding to One Nation's attack on the ,mining division of the CFMMEU, the union's national president, Tony Maher, wrote to Senator Roberts and the Queensland Liberal National chair of the committee holding Wednesday's hearing, Senator James McGrath, to defend the union's position.

Referring to the union's joint control [with the employer peak body, the minerals council] of "a range of industry bodies, Mr Maher said suggestions this was "somehow detrimental to workers' interests" was "complete rubbish".

"The union uses its involvement in industry bodies to actively represent the interests of workers in the coal industry," Mr Maher said.

"No financial dividend from our partial ownership or involvement in any industry body, other than director fees where these are paid, flows back to the union."

During Wednesday evening's questioning of the general manager of the Fair Work Commission, Bernadette O'Neill, Senator Roberts said various enterprise agreements used to employ casuals at Hunter Valley coal mines left them "far worse off" than permanent workers, with lower hourly rates than the ruling Black Coal Award, and "no annual leave, no sick leave, no redundancy, no accident pay".

He said enterprise agreements were also not allowed to introduce employment classifications - in this case "casual" production workers - that did not exist in the award.

"How can this be?" Senator Roberts asked, arguing that the enterprise agreement he was referring to meant that "casual" labour hire mine workers doing the same work on the same rosters as their directly employed colleagues were left "far, far worse off".

Ms O'Neill agreed that enterprise agreements needed to pass the "Better Off Overall Test" (the BOOT). She said she could "not speak hypothetically" but the BOOT test was the condition the Fair Work Commission used "in deciding whether to approve an agreement".

She twice declined to accept a briefing from Senator Roberts on the details of the cases he was talking about.

As the Herald reported yesterday, the deputy chief executive of the Coal Mining Industry (Long Service Leave Funding) Corporation, Suzanne Jenkins, told Senator Roberts during their hearing that she only knew of one formal complaint about a long service leave account.

Against this, Coal LSL's 2018-19 annual report revealed 659 requests from mine workers for "reviews" of long service leave accounts, up from 515 in 2017-18.

Responding to questions from the Herald, Coal LSL chief executive Darlene Perks said the 659 reviews were not "formal complaints".

"These reviews are about historical or current recognition of service and we encourage employees in the industry to have any missing service assessed for eligibility," Ms Perks said.

"We do not have the power to adjudicate in disputes between employees and employers; these matters lay with the Fair Work Commission as stated in the legislation."

Senator Roberts had asked Fair Work's general manager, Bernadette O'Neill, why Coal LSL referred complaints about long service leave accounts to her organisation, but she was unable to answer, saying: "Senator, I'm sorry, it's just really difficult to answer in the abstract."

In his statement after the hearings, Senator Roberts said One Nation would "have more to say" about problems in the coal industry because the party was "committed to protecting workers, their rights and their entitlements".

But the CFMMEU's Tony Maher questioned this in writing to Senator Roberts, saying: "If your concern is genuine, I suggest you take up these issues with mining companies like BHP who are driving the casualisation agenda; and the Morrison government, which could change the law to prevent casual exploitation but chooses not to.

"However, we realise this would be inconsistent with your party's anti-worker record."

Mr Maher said Senator Roberts had his "facts wrong in a number of areas".

"At the heart of your questioning was the assertion that because the Black Coal Mining Industry Award does not recognise casual employment, it is therefore illegal for coal miners to be employed casually," Mr Maher wrote.

"This is just not true.

"However much we disapprove of casualisation, coal miners may be employed under enterprise agreements that allow for casual work as long as they are approved by the Fair Work Commission.

The commission regularly approves EAs that include provisions for casual employment despite union arguments it is detrimental to employees, accepting that a pay increase of as little as 1 per cent over the award is enough to leave them better off overall."

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