Tony Abbott's handpicked royal commissioner into trade union corruption, Dyson Heydon, will rule on Friday on whether any application from unions to disqualify him has merit.

The situation in which a royal commission will judge its own impartiality and fitness to continue comes as Mr Heydon, a former High Court judge, admitted to knowing of, and then forgetting about, Liberal Party ownership of a function he agreed to address later this month.

The startling admission regarding the now-abandoned address came during a tense day in which counsel acting for the ACTU sought full correspondence regarding Mr Heydon's agreement to give this year's Sir Garfield Barwick Address to the Liberal Party Lawyers and Legal Policy Branch.

Unions and the ALP believe the links between Mr Heydon and the Liberal Party suggest bias that renders him unfit to continue in the $80 million inquiry.

In Parliament the opposition directed every question at the government over the issue, arguing Mr Abbott should relieve him of the commission.

Mr Abbott defended Mr Heydon as a man of impeccable integrity, while refusing to be drawn into the specifics beyond denying that the event in question had been a fundraiser for the Liberal Party.

Labor has branded the commission a "political witch-hunt", with its manager of opposition business, Tony Burke, leading the question time attack.

"Doesn't this make it clear that the royal commission had been politicised from the start and the Prime Minister should withdraw Mr Heydon's commission?" he asked in Parliament.

Mr Abbott said the royal commissioner had cancelled his planned lecture as soon as he learnt it was being organised by the NSW Liberal Party, even though Mr Heydon himself had admitted knowing it was a Liberal Party function when approached last year.

"After Mr Heydon became aware that it was a Liberal-badged event, he withdrew," Mr Abbott said.

But emails released by Mr Heydon reveal he was sent the flyer promoting his speech, which features the Liberal Party logo and a donation form, as well as information about declaring electoral donations, as early as June 12.

Mr Heydon was forced to interrupt the Monday hearing to explain how he had "overlooked" the Liberal Party's connection.

Speaking from the bench, he explained that he was approached on April 10 last year to give the keynote speech.

However, when he received a follow-up email in March this year he had forgotten key details.

"I overlooked the connection between the person or persons organising the event and the Liberal Party which had been stated in the email of 10 April of 2014," he said.

"I also overlooked the fact my agreement to speak at that time had been conditional on the work of the commission being completed before that time."

In response to an ACTU request for all documents relating to the fundraising event, Mr Heydon on Monday released emails he received from Gregory Burton, the chairman of professional engagement for a lawyer branch of the NSW Liberal Party. Mr Burton's email of April 10, 2014, declared the lawyer branch was formally a branch of the party, but its aim was to be a "liberal minded bridge to the profession rather than overtly party political".

"Although we trust we show the party in a favourable light!" the email said.

Mr Heydon said the April 10 email "did not state and I did not understand from it that the Sir Garfield Address was in any sense a fundraiser for the Liberal Party".

"The email stated that it was organised by a body which I was told was 'one of the lawyer branches of the Liberal Party NSW division', which had a focus on ... professional engagement."

Mr Heydon said he did not turn his mind to the address again until he was reminded of it in March this year.

He said he looked at details of when and where the event was to be held but did not open email attachments that detailed the fundraiser because he was busy with the royal commission's hearings.

Last week he said he could no longer attend after it was made clear it was a fundraising event. Emails show Mr Heydon had planned to speak about the "judicial stature" of Sir Garfield Barwick "viewed in modern perspective".

The ACTU's barrister, Robert Newlinds, SC, said the ACTU had asked for documents relating to the August fundraising event in preparation for making an application for Mr Heydon to disqualify himself from the royal commission.

Mr Heydon questioned Mr Newlinds' legal standing to make the application. The ACTU has not appeared before the commission and is not among unions named as part of the terms of reference.

After an adjournment, Mr Newlinds asked to be excused because he had no further instructions from the ACTU about whether he should proceed with the application seeking Mr Heydon's disqualification from the royal commission.

Senior counsel assisting Jeremy Stoljar said: "This is degenerating into a shambles... on the part of the ACTU." He said Mr Newlinds' application to be excused "smacks of grandstanding".

Mr Newlinds said: "The last thing I have tried to do is to grandstand or make this a farce."

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