The former high court judge Dyson Heydon will face his accusers on Friday when unions ask him to disqualify himself from the royal commission into trade union governance and corruption because of an alleged appearance of bias.



Heydon, the sole commissioner, is due to begin the hearing in Sydney at 10am when he will consider three submissions asking for his recusal.



The Australian Council of Trade Unions has lodged an application on behalf of Unions New South Wales and four unions – the Health Services Union, the Transport Workers Union, the Maritime Union of Australia and the CEPU, which represents plumbing and communications workers.



The push is supported by the CFMEU and Australian Workers Union, which have lodged their own submissions.

Heydon has signalled he may not make a decision at the hearing on Friday.

A spokesman for the commission said if Heydon did not determine the application at the conclusion of the oral hearing “he will deliver his ruling as soon as possible thereafter, possibly on Tuesday 25 August”.

It was wrong to agree to attend Liberal party events when you stand in judgment of the Liberal party’s political rivals Labor leader Bill Shorten

The fate of the commission hangs in the balance because of an outcry from Labor and unions after revelations Heydon initially accepted an invitation to speak at a Liberal party fundraiser.

Heydon, who pulled out of the Sir Garfield Barwick address last week, said he had “overlooked” the Liberal party connection when he was contacted by the organiser in March 2015, and also overlooked the fact his agreement in 2014 to speak at the event had been conditional on the commission’s work having been completed.



In an explanation on Monday, Heydon said he had not read the attachments of a June 2015 email that contained an invitation and Liberal party donation information, but his “understanding at all times has been that the dinner was not to be a fundraiser”.



The prime minister, Tony Abbott, continued to defend Heydon in parliamentary question time on Thursday, saying the Labor party was “smearing a distinguished Australian” because it was “only interested in protecting dodgy union officials”.



“He has given distinguished service to our country and he continues to give distinguished service to our country, exposing the rorts, the rackets and the rip-offs that have been covered up for too long inside the Australian trade union movement,” Abbott said.

The Labor leader, Bill Shorten, said Abbott should have acted to withdraw Heydon’s commission, rather than putting “his captain’s pick in the position where he decides himself if he is fair or unfair”.

“It is wrong for a royal commissioner investigating the political rivals to accept an invitation to a Liberal fundraiser,” Shorten said.

“That is not what we expect for impartiality of judges and commissioners. No matter how distinguished and honourable, it was wrong to agree to attend Liberal party events when you stand in judgment of the Liberal party’s political rivals.”

Shorten, a former AWU Victorian and national secretary before his entry into federal parliament, was questioned by the commission during two days of hearings in July. Heydon questioned his credibility as a witness at one stage during those proceedings.

Shorten said on Thursday he was not opposed to the royal commission continuing with a different commissioner. “The key issue here is the captain’s pick, the royal commissioner, and Tony Abbott. If they find another royal commissioner, so be it,” he said.

The commission is due to finish its final report in December this year.