In the House of Representatives last week, Mr Fitzgibbon backed Coal Services and Coal Mines Insurance, the formerly government owned bodies that Senator Roberts is criticising because of their joint ownership by the Minerals Council of NSW and the CFMMEU, which he says is a conflict of interest.

Mr Fitzgibbon said the idea that the union and Coal Services "have somehow conspired to deny injured coalminers the support they deserve . . . is absolute rubbish".

As well as looking after workers, the industry bodies had overseen "impressive" reductions in injury rates.

"Now while some might be open to the idea that a coal company might be interested in prioritising profit over people - not something I subscribe to - surely no-one would believe that the union is capable of such thinking," he explained.

"Over the course of the last month, the Newcastle Herald has run a series of articles based on speeches made in the other place by Senator Malcolm Roberts from One Nation," Mr Fitzgibbon said.

Further reading: Coal Shoulder part one and part two

"Senator Roberts has asserted that both the miners union and I have failed in our duty to offer support, advice and protection for our local coal miners.

"Nothing could be further from the truth.

"Senator Roberts has asserted I had failed to adequately support local coalminers who have suffered injury in our local coal mines.

"I reject this assertion absolutely, and my records put pay to this lie."

He said Senator Roberts was right to criticise casual employment in the industry but he had no solutions and was not backing Labor's.

He said if Senator Roberts was serious, One Nation could withdraw its vote from the Coalition until the government fixed the casuals issue.

Mr Fitzgibbon acknowledged on Sunday that his Thursday speech was shortly before Senator Roberts and One Nation leader Pauline Hanson shocked the government by joining with Tasmanian Senator Jacqui Lambie to defeat the Coalition's Ensuring Integrity Bill, which Labor views as union-bashing.

Asked about this, Mr Fitzgibbon said he was hoping for more One Nation votes against the government.

Injured Hunter mineworker Simon Turner, referred to in parliament by Senator Roberts, says Mr Fitzgibbon and other critics should look at the substance of the concerns, rather than shoot the messenger.

He said unions were quite capable of putting their own financial interests ahead of their members, as shown by the large and questionable payments from employers revealed in the 2014 trade union royal commission.