Union corruption royal commission resumes, whistleblower faces questioning over alleged slush fund

Union whistleblower Kathy Jackson will return to the witness box today when the royal commission into union corruption resumes.

The Health Services Union (HSU) national secretary made accusations about rampant corruption by now-jailed HSU general secretary Michael Williamson, who kept the union's accounts shrouded in mystery.

In previous hearings, Ms Jackson detailed extensive intimidation by union officials intent on discrediting her.

She was ostracised, called a traitor and a rat, received a midnight death threat and wound up in a psychiatric hospital.

But during the commission it emerged Ms Jackson set up the unaudited National Health Development Account with union money and allegedly accessed it for personal spending.

The Royal Commission into Trade Union Governance and Corruption has investigated the Australian Workers Union, Transport Workers Union and Construction, Forestry, Mining and Energy Union since it began in April.