Labor is demanding the resignation of the head of the royal commission into union corruption, following revelations he agreed to speak at a Liberal Party fundraising event.

Commissioner and former High Court judge Dyson Heydon was advertised as the guest speaker at the $80-a-head Sir Garfield Barwick address in Sydney later this month.

The event was organised by the legal branch of the New South Wales Liberal Party and first advertised in April.

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The politically-branded invitation promoted Justice Dyson’s appearance and offered guests the option to make cheques “payable to the Liberal Party”, saying proceeds would be “applied to state election campaigning”.

Earlier on Thursday, Justice Heydon confirmed he had cancelled his attendance. His office also released a series of emails showing he was previously assured by the organisers that it was not a fundraiser.

Tony Burke labelled the royal commission a farce.

But the manager of opposition business Tony Burke said the commissioner had revealed deep bias and partisan links.

“He is conflicted, he is biased, the royal commission is a farce,” Mr Burke said.

“Dyson Heydon is in a position now where he cannot remain in that role.

“The sham – that we have said for so long this royal commission was – has now been found out and exposed.”

Labor has repeatedly accused the Government of waging a political witch-hunt through the royal commission, particularly by calling Opposition Leader and former union official Bill Shorten before the hearings earlier this year.

But PM Tony Abbott says it is beyond reproach. Photo: AAP

But the Prime Minister said the Government would “defend the integrity” of Justice Heydon and the union corruption probe.

“The behaviour of the royal commissioner has been absolutely beyond reproach,” Mr Abbott said in Question Time.

The leader of the house Christopher Pyne told Parliament the Opposition’s campaign would backfire by drawing more attention to Labor’s links to questionable union behaviour.

“What a spectacular own goal,” Mr Pyne said.

“Labor finds themselves on the side of bashing the umpire on this occasion, of taking out a political baseball bat and attacking the umpire.”

Director of the New South Wales branch of the Liberal Party, Tony Nutt, said for Labor to suggest the speech was a “significant fundraising event is ridiculous”.

Despite that, shadow attorney-general Mark Dreyfus has threatened court action if Justice Heydon does not resign.

“Now we have, if more were needed, absolutely clear proof of the association between this royal commissioner and the Liberal Party of Australia,” he said.

“The first step is to raise the matter with the royal commissioner.

“If the royal commissioner refuses to disqualify himself formally, it’s a matter that can then be taken up in the court, almost certainly the Federal Court of Australia.”

The Greens have called for the royal commission to be “immediately terminated”.

“If a judge was found to be raising funds for the prosecution there would be a mistrial and the case would be over. That is what has to happen here,” Greens MP Adam Bandt said.

“Any pretence of independence of the trade union royal commission is now gone and the royal commission must be immediately terminated.”

– ABC