HSU's Kathy Jackson questioned by former lover at royal commission

Health Services Union (HSU) whistleblower Kathy Jacksonhas beencross-examined by a lawyer she had an affair with after her application to stop the questioning was struck out.

Her lawyer hadearlier asked the royal commission into trade unions that Ms Jackson not be questioned by barrister Mark Irving, because she believed he would be hostile to her due to the affair.

In an affidavit presented to the commission, the now HSU national secretary said the affair happened more than 20 years ago when she was married to her first husband, and the marriage was "abusive".

She said after six weeks she "pulled back" as she did not want to destroy her marriage.

However, commissioner John Dyson Heydon rejected her application, saying he did not think the affair would affect Mr Irving's professionalism.

"The fact that a barrister had an affair with a colleague more than 20 years and carried out professional duties ... two years ago does not suggest that Mr Irving will not be objective, nor does it suggest that he will be hostile to the point of furthering a personal vendetta," he said.

The commissioner also said if Ms Jackson "did have the beliefs and fears about Mr Irving that she claims to have, she would have protested at the time when Mr Irvine first announced his appearance."

Ms Jackson is appearing for a third time at the Royal Commission into Trade Union Governance and Corruption.

On Wednesday, the commission heard from her ex-husband, Jeff Jackson, who said a $50,000 payment made to him out of a slush fund account she set up with HSU funds was for a property settlement in their divorce.

However, in a statement to the commission Ms Jackson said it was for fighting a union election at the HSU's first Victorian branch.

Counsel assisting Jeremy Stoljar SC asked Ms Jackson on Thursday why withdrawals made from the account totalled $102,000 - the exact amount she owed Mr Jackson in family law orders.

But Ms Jackson denied it was for the same amount and said she paid the divorce settlement with her own and her parents' money.

She was also questioned about an $80,000 payment made out of the account in 2005, which Ms Jackson said was for a study trip to the United States.

The commission has previously been told the account was set up with a $250,000 payment from a Victorian cancer centre.

It heard on Thursday an invoice to the centre for legal fees was overinflated by more than $64,000.

But Ms Jackson said that was to recover union expenses in negotiating an agreement for staff.

The royal commission continues.