With Labor opposing the bill as "union bashing", the government is relying on One Nation's support for it to pass. Senator Roberts did not indicate whether he would support or oppose the bill during his speech, although he did thank Senator Marise Payne for her "interest" in the Mount Arthur issues.

Expanding on a Senate speech made earlier this month, Senator Roberts referred to the Newcastle Herald's reporting on Mount Arthur, and said the Attorney-General's Department had "confirmed" One Nation's "analysis" of a range of issues that he and the barristers working with the party had raised with government officials.

"The CFMMEU approved the substandard conditions and pay rates of the so-called casual miners working on coal production even though they worked the same hours, roster and duties as the full-time production workers who worked beside them at Mount Arthur." Senator Roberts said.

He read from an April 2015 letter from Chandler Macleod to the head of the mineworkers' union in the Hunter, Peter Jordan, proposing that as a condition of resolving a dispute at Mount Arthur, the union would "cease from any current and future actions and claims ... towards ventilating and agitating its view that ... Chandler Macleod ... casuals ... may be entitled to leave and other entitlements ... or that Chandler Macleod is not paying its employees their lawful terms and conditions".

"In other words, drop it, and the union agreed," Senator Roberts said.

He said "everyday Australians expect to see honest employer and employee organisations, honest unions, to be free to thrive".

"At the same time they want the rogue organisations to be held accountable for exploiting union members for personal and/or political gain and power."

Senator Roberts thanked injured former Mount Arthur mineworker Simon Turner, who has previously said he turned to One Nation for help after both major parties ignored him.

Referring to Mount Arthur, Senator Roberts said: "One person was told that the mine had had a large number of safety incidents and that if he reported his injury and his incident he would be fired.

"He'd lose his income. These people and others have shown authorities documentary evidence that their injury was not correctly reported, yet BHP, Chandler Macleod, the NSW Government and the CFMMEU don't care."

Senator Roberts said he had three aims.

He wanted the "exploited" casuals to receive their "fair entitlements" as well as compensation for suffering and trauma.

He wanted the union/employer "rorts" stopped immediately and he wanted penalties for the perpetrators of the "BHP/Chandler Macleod/CFMMEU scam".

The Newcastle Herald approached mineworkers' union district president Peter Jordan last month about the clause in the April 14, 2015, letter from Chandler Macleod to the union that Senator Roberts raised in parliament on Wednesday.

We asked about the letter, because it was put to us that it was a "gag" clause - that the union was agreeing to "go quiet" on Chandler Macleod's pay and conditions at Mount Arthur.

The union responded by saying it did not agree to the clause, which was not a "gag" clause. The union said it did not refer to the union criticising Chandler Macleod, but to the union agreeing not to take legal action against it.

It said it did agree not to take legal action for a period, and "instead" negotiated backpay of $3 an hour, which it said was "substantially more financially beneficial" than "backpaid award leave entitlements would have been".

Mr Jordan provided a copy of the letter sent with his signature in response, the following day, April 15, 2015.

In that letter to the head of Chandler Macleod's employee relations department, Tory Kakoschke, Mr Jordan said the "assurance sought from the union" in relation to the clause in question went "beyond the circumstances relating to" the Mount Arthur employees working as casuals without "an enabling provision" in the award.

The letter then said "we would be happy to provide the assurance sought" as long as Chandler Macleod understood it did not stop the union from taking action where" according to law, the employee was not properly classified as a casual".

This is a reference to one of the major issues of the Mount Arthur debate, and of casual employment in NSW and Queensland coalmining in general.

Despite the existence of dozens of enterprise agreements based on or including casual employment, the Black Coal Mining Industry Award 2010 says only some types of staff can be employed as casuals, with all others either full-time or part-time, as Senator Roberts has referred to repeatedly in parliament.

The lawyers behind the Mount Arthur class action that has Simon Turner as its lead claimant is understood to be based on the same legal argument, that enterprise agreements including "casual" employment are unlawful, even though they have been approved by the Fair Work Commission.

Simon Turner at head of coal class action

Union says BHP 'sneaky' over 'Operations Services' jobs

Malcolm Roberts first raising of Mount Arthur in parliament

Union hits back at Roberts over 'bizarre' claims

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