Nicknamed "the million-dollar man", Williamson, who has been jailed for at least five years for fraud, ran the union for 16 years until a Fairfax Media investigation in 2011 revealed his cronyism and corruption.

Gerard Hayes, who was elected as secretary of the HSU NSW in 2012, told the royal commission on union corruption on Tuesday that Williamson was still playing an active role long after he officially stood down in late 2011.

When counsel assisting the royal commission, Jeremy Stoljar, SC, suggested Williamson was still in control of the union until early April 2012, Mr Hayes said: "It could have been a little bit beyond April as well."

Fairfax Media's revelations sparked an internal investigation led by barrister Ian Temby, QC, that showed Williamson and his family received more than $5 million from the union in the previous few years alone.

A recording of an intercepted phone call between Williamson and Mr Hayes on April 4, 2012, played during the commission hearing reveals Williamson's explosive demeanour at the time. It also reveals that ALP Federal Senator, Sam Dastyari, who was the NSW ALP boss at the time, tipped off Mr Hayes about a government plan to send in administrators to clean up the union.

During the conversation, Williamson launches into a tirade of expletives as he accuses Mr Hayes of "treachery" for planning a meeting without him or acting general secretary Peter Mylan.

When Mr Hayes tells Williamson of government plans to put the union into administration, Williamson says "they can't" and demands to know who told him. Mr Hayes says the information source was Mr Dastyari.

Williamson later accuses Mr Hayes of blowing the union up before making what is a likely reference to HSU whistleblower Kathy Jackson.

"Well, mate, you've just f---ing blown the whole f---ing house up ... because of your f---ing paranoia about stuff that's not there. We've got this sheila on the f---ing rack, we've got her on the f---ing rack, we've got Temby on the f---ing rack and you're going to f--- it up.

"And if you think I'm not f---ing pissed off with you, mate, it's a f---ing understatement."

Earlier during the hearing, Diana Asmar, president of the HSU Victoria No. 1 branch, denied allegations that she directed a colleague to cheat on tests for other union officials.

The commission heard evidence on Monday that Ms Asmar allegedly instructed employees Pik ki (Peggy) Lee and Kimberley Kitching, an unsuccessful ALP candidate, to complete online tests on behalf of other colleagues. The tests were for permits that give union officials the right to enter a workplace without the risk of trespass.

Both Ms Kitching and Ms Asmar denied the accusations.

In a sworn statement, Ms Kitching said: "I have never conducted any test for a right of entry training course, either for myself or for any person. Neither Diana nor any other person has ever asked me to conduct such a test for themselves or for anyone else."

She also accused some of the witnesses of being politically motivated in the lead-up to HSU Victoria elections later this year.

Ms Asmar said she completed her own test and denied instructing Ms Kitching to do the test for others.

When asked about consecutive sackings of union staff and the hiring of replacements on much higher salaries, Ms Asmar agreed with Mr Stoljar's proposition it was within her authority to "hire and fire people at will".

"As per the rules, yes," she said.

Asked about her decision to hire her supporter Ms Kitching on a salary of $110,000 to $120,000 without advertising the position, Ms Asmar said she had done so with the approval of the branch committee of management.

Kathy Jackson and her former husband Jeff Jackson will be called this week to give evidence about a $50,000 cheque Ms Jackson paid Mr Jackson from a slush fund linked to the union.