Union whistleblower Kathy Jackson has likened an investigation into her alleged misuse of union members' funds to "judicial gang rape", and dismissed a past fling with one interrogator as a "charity shag".

Ms Jackson, who is on leave as the national secretary of the Health Services Union, finished giving evidence to the Royal Commission into Trade Union Governance and Corruption on Friday by saying she would not try to expose union corruption again.

She said she "could not believe the audacity" of one-time lover Mark Irving, now the barrister for the Health Services Union (HSU), cross-examining her before the commission about her alleged improper use of union funds.

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She had fought to prevent Mr Irving questioning her, claiming he would be biased - a claim rejected by the commission.

But after completing her evidence, she dismissed their brief affair of 21 years ago.

"Forget the former lover stuff - everybody makes mistakes and has a charity shag along the way," she said.

Ms Jackson said she understood the community concern about union slush funds like one she operated as national secretary of the HSU.

But she said her detractors at the HSU had pursued her unfairly.

"These people at the Health Services Union rely on a judicial gang rape of Kathy Jackson because they can afford to do it; they've got lawyers, guns and money," she said.

She later apologised for the use of the term "gang rape".

"I was referring [to] the actions the union, the Health Services Union, are taking against me in the Federal Court on numerous fronts, not only this year but in previous years," she told Macquarie Radio.

"But I just want to apologise, and I realise it's offensive to refer to what has been happening in the judicial system as that."

Union funds 'protection' for members: Jackson

The commission has investigated Ms Jackson's use of a $280,000 union fund known as the National Health Development Association - including a $50,000 withdrawal that was paid to her ex-husband.

Ms Jackson said all unions and union officials should be investigated like she had been.

"They should be looked into because I understand now the community concern," she said.

"But the reason they're there and the reason they were set up, not just in my time but before my time, is to get around electoral disclosure."

Ms Jackson said funds were needed to protect the union from "vultures" in the Labor Party "that are circling these unions to take them over".

Asked if she was playing along with the game, Ms Jackson said, "of course I was".

"But it was more than that - I was buying protection for my members," she added.

Ms Jackson has been excused from the commission, which will continue next week with an investigation of the Construction, Forestry, Mining and Energy Union.

AAP/ABC