HSU boss Kathy Jackson clashes with ex-lover on the witness stand

During a tense cross-examination by her former lover, HSU boss Kathy Jackson has admitted signing a cheque granting herself a $63,000 ex gratia payment - even though she had no authority to do so.

Ms Jackson had earlier applied to stop her cross-examination by union barrister Mark Irving, with whom she had an eight-week affair 21 years ago.

But this was rejected by the Royal Commission into Trade Union Governance and Corruption, which ruled the past sexual relationship was irrelevant.

Mr Irving then asked her about the merger of the Victorian and NSW union branches in May 2010.

Ms Jackson was branch secretary of the Victorian No. 3 branch but after the merger, became general secretary of the Health Services Union East branch.

Mr Irving said funds which were the property of the Victorian branches then became the property of the HSU East branch.

By May 2010 Ms Jackson was no longer branch secretary but on June 30 2010, she signed a $63,000 cheque, which was an honorarium for herself.

In reply to questioning from Mr Irving, she said although the amalgamation had gone ahead, the funds had not been consolidated.

"They were not hidden accounts," she said.

She also said she did not inform the national executive because they did not usually get reports from autonomous branches.

Mr Irving asked Ms Jackson if there had been "remittance for any taxation to the Australian Tax Office?"

Ms Jackson said she would have to check as she hadn't been prepared for the question.

"If you want to delve into my tax affairs, feel free," she added.

In earlier evidence Ms Jackson had said she could not remember the details of large withdrawals of union money, one of which happened before a trip to Hong Kong.

She also denied she used union funds to pay off her credit card after she went on a trip to the US.

Mr Irving told Ms Jackson proceedings had been commenced against the union for failing to file returns on donations.

He said the proceedings arose out of the conduct of the Victorian No.1 branch between 2008 and 2009 and would incur penalties.

The union is suing Ms Jackson in the federal court for the penalties.

The hearing continues.