Unions royal commissioner Dyson Heydon could again delay a decision on his future following claims about withheld information.

Mr Heydon is currently scheduled to deliver a ruling in Sydney on Monday on whether he should stand down from the inquiry into union corruption.

But the ruling, which was originally planned for August 25, could be delayed again as unions seek to clarify information previously not disclosed by the commissioner.

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On Thursday, the commission released two emails and a note of a conversation which related to Mr Heydon’s acceptance of an invitation to speak at a Liberal Party event – the Sir Garfield Barwick address.

ACTU secretary Dave Oliver described the emails as a “vital bit of information” which had been withheld when the union peak body initially applied to have Mr Heydon disqualified over perceived bias.

“One thing’s for sure, this royal commission has been irreparably tarnished,” Mr Oliver said on Friday.

Unions had until 5pm (AEST) on Friday to make written submissions about the new evidence.

“There might be further delays, given there’s been three already,” Labor workplace spokesman Brendan O’Connor told reporters in Melbourne.

“But we said two weeks ago … any fair-minded observer would conclude that he (Mr Heydon) was not in a position to continue, because at the very least there was an appearance of a conflict of interest as a result of his association with the Liberal Party.”

Solicitor for the commission Peter Gordon said the commissioner did not “presently apprehend the relevance of the (new) documents” to the unions’ bid to have him step down, but was happy to allow time for them to be considered.

On August 12, the NSW Bar Association’s publications manager Chris Winslow received a phone call from former journalist and lawyer Marcus Priest expressing surprise at Mr Heydon’s acceptance of the invitation to deliver the August 26 address, when it was clearly being organised by the NSW Liberal Party’s lawyer branch.

Mr Winslow then emailed Jeremy Stoljar SC, the counsel assisting the royal commission.

“Is Dyson Heydon aware that the Garfield Barwick Address, which he is due to deliver, is a Liberal Party fundraiser?” read the email.

Mr Stoljar replied that he would raise it with the commissioner.

Mr Stoljar did not show the emails to Mr Heydon, but made a note of a meeting with the commissioner at 9am on August 13.

He wrote of the meeting that Mr Heydon had shown him an email dated August 12 from the event organiser, lawyer Greg Burton, which stated it is “not a fundraiser”.

“Burton is closer to the action than Winslow – he ought to know,” Mr Stoljar noted.

“So OK to go ahead if JDH (Heydon) writes clarifying + response OK.”

The commission heard last week that the August 12 email from Mr Burton – which Mr Heydon had read – stated the dinner is “nominally under the auspices of the Liberal Party lawyers’ professional branches”.

Prime Minister Tony Abbott stood by the commissioner, saying other judges had addressed Liberal and Labor events in the past.

– AAP