He spent Tuesday and half of Wednesday being grilled in Sydney by the trade union royal commission's Sarah McNaughton, over allegations his organisation uses a complex web of proxies to conceal lucrative deals with an inhouse trust, a mandatory charity, a training organisation and The Tradies Group.

The ACT CFMEU branch secretary already had the dubious distinction of being the boss of the only union branch to date where investigations initiated by the commission have led to the arrest of officials and former officials.

While he was in the witness box in Sydney on Wednesday, high-profile ACT CFMEU organiser and former Canberra Raiders star John Lomax was making a well-publicised appearance in the Canberra Magistrate's Court on a charge of blackmail. Mr Lomax has lodged a not guilty plea.

The charge arises from an allegation Mr Lomax forced a Canberra painting company, Nel Trading, and its principal, Woong Yul Park, to sign a CFMEU enterprise agreement in April 2014.

Mr Park allegedly believed he would be blocked from working in the ACT and NSW if he didn't sign.

This is consistent with claims made by multiple employers engaged in concreting, formwork and other trades at the Canberra hearings in July.

Lawyers representing the CFMEU have repeatedly argued it was the job of the union's organisers to negotiate the best wage deals they could for their members.

Fairfax understands the "financial disadvantage" Mr Park suffered as a result of signing the CFMEU EBA was that he had to pay workers $26 an hour when he claims that without it he could have paid as little as $17 an hour. This is under the current national minimum wage rate.

The ACT CFMEU branch is also dealing with the ongoing fallout from the arrest of a former organiser, former ALP sub-branch president and former Woden Tradesmen's Union Club director, Halafihi "Fihi" Kivalu.

Mr Kivalu has pleaded not guilty to two charges of blackmail arising from his admission at the commission's hearings in Canberra last month he had accepted more than $100,000 from builders who believed he would use his union position to help them win major contracts.

CFMEU lawyers told the hearing CFMEU bosses had no knowledge of Mr Kivalu's activities.

The same hearings were told of alleged standover tactics, interrupted concrete pours, price-fixing cartels and pressure being applied to building companies operating in Canberra to sign "non-negotiable" pattern-bargained enterprise agreements.

On the eve of his royal commission appearance, Mr Hall texted his supporters to say the fight was just beginning.

"Our branch has been under an unprecedented attack by conservative forces," the former history teacher said.

"The attack is not over but fight for our union is strong. `The battle has now begun. Our hearts are beating. The fight is just. Our spirit will triumph'."

Before Mr Hall left the witness box on Wednesday Royal Commissioner Dyson Heydon warned him he would be expected to return in the last week of August, to give evidence on the many matters raised at the Canberra hearings.

"Mr Hall, you can leave the witness box now. I think, though, you will have to come back later to discuss the evidence of the last three weeks or so in Canberra," Commissioner Heydon said.

Having just endured 12 hours of forensic examination by counsel assisting the commission, Sarah McNaughton, SC, this was likely the last thing Mr Hall wanted to hear.

Ms McNaughton repeatedly put it to him deals had been struck on the basis of what was good for the union's balance sheet, not the welfare of its members.

Mr Hall, himself a sophisticated media performer who has been on the front foot in tackling the issue of high levels of death and injury on ACT construction sites since he replaced Sarah Schoonwater as the branch secretary in 2007, would have none of it.

"I only operate in the interests of the members, their families and the communities they live in," he said.

This, on its own, appears unlikely to be sufficient to derail the commission's well-crafted narrative of a pragmatic union whose officials dragooned employers into agreements, locking in lucrative training, charity and income protection deals with its own proxies, which then channelled the hundreds of thousands of dollars raised back to the union.

That narrative is the product of the commission's by now well-oiled modus operandi.

Evidence has been collected by investigators, members of police task forces and counsel assisting the commission from a wide range of sources, including phone taps and informers.

This information has been used to prepare a brief in the form of a statement of what counsel assisting asserts to be the case.

In the Canberra hearings, witnesses (including union officials on the one hand and many employers who on their own admission were openly hostile to unions, unionism and the ACT CFMEU in particular on the other), were interrogated in a court-like environment where normal rules of evidence did not apply.

Union lawyers repeatedly objected to "fishing expeditions" - instances where witnesses were being led by counsel for extended periods - and the introduction of material into evidence that would not be admissible in a court of law, only to be told by Commissioner Heydon he was "happy to see where this leads".

This appears to create the risk that when the commission's findings are handed down they could be a "self-fulfilling prophecy" and, as a result, open to question and possibly irrelevant.

Mr Hall believes the real test of the commission's work will be which, if any, of its assertions are upheld in courts where individuals have the usual rights and protections accorded those accused of a crime.

Despite its inquisitorial powers, the commission's investigations have, to date, only resulted in the arrests of Mr Lomax and Mr Kivalu.

The third Canberra arrest was in regard to alleged perjury and raises the question of whether or not contractors who denied involvement in alleged price fixing will face similar charges.

If no further arrests are made and Mr Lomax or Mr Kivalu are acquitted, the question will be whether the $60 million to $80 million spectacle - admittedly a colourful spectacle, which even put the leader of the federal Opposition in the witness box - was worth it in a time of financial austerity.

This week's hearings in Sydney were built around a complex chart listing 11 different organisations controlled by the ACT CFMEU and The Tradies group and connected by interlocking directorships and funds transfers.

Mr Hall is either a director, committee member or recent director of nine of these bodies.

Stephen Brennan, the chief financial officer of The Tradies Group, is on seven boards or management committees and Jason O'Mara, the ACT CFMEU assistant secretary, is or has been on eight.

"The question arises as to whether the setting up of these complex structures in relation to these three areas - training, contribution to a charity and income protection - was done deliberately to hide the CFMEU's involvement in and or connection with the entities or structures set up to provide these services," Ms McNaughton said.

While, on the face of it, the money trail could be construed as suspicious, it has to be said there is a certain "no shit Sherlock" quality about the revelation that The Tradies clubs work closely with the ACT CFMEU branch.

Both clubs include the words "Tradesmen's Union Club" in their registered names and, as Mr Hall pointed out on Wednesday, their joint community fund was intended to support the CFMEU and CFMEU members from the get-go.

Clauses seven, eight and nine of the community fund's constitution list assisting in the training and development of people entering or already employed in the construction, forestry, mining and energy industries and to further the objectives of the labour movement as legitimate objectives.

The same clauses appear in the constitutions of the clubs themselves.

The union branch, in turn, subcontracts much of its administrative and financial work out to the larger and better resourced The Tradies Group management team to save money and keep staff levels down.

That said, the detailed examination of what is a demonstrably lucrative relationship provided interesting context for Canberra builder, Dennis Milin's, testimony on July 22 that his firm was kicked off a $90 million residential tower-block development in 2012, because the CFMEU didn't like him.

IQ Apartments, on Northbourne Avenue, is a seven-storey, 230-unit development which is offering apartments for immediate occupancy from $415,000.

Mr Milin said everything was going well until The Tradies Group, "as represented by Mr Dean Hall of the ACT CFMEU branch and the financial controllers of the Tradies Group", came in as an investor at the 11th hour.

"On February 12, 2012, Milin entered into a preliminary contract with PrimeSpace as the principal and Milin as the builder," Mr Milin said.

"PrimeSpace could not achieve sufficient pre-sales to satisfy its lenders and decided to bring in a joint venture partner known as The Tradies Group."

Mr Milin met Mr Hall and the CFMEU branch assistant secretary, Jason O'Mara, in March or April, 2012.

He said: "Dean Hall said `who would ever imagine we would be working together'."

The union officials also said Milin would need to have a union enterprise agreement and that all of its contractors would need to have union agreements.

"I said: `I am not sure about that, to the best of my knowledge as a developer people want to pay less, not more'."

Mr Milin said the officials told him they wanted contractors they "had a relationship with".

"They [Mr Hall and Mr O'Mara] said `every four years we have a vote and we need those votes to hold our positions, and that is more important than the construction price. If you engage contractors without EBAs and union memberships that will upset our relationships and risk losing votes'."

Mr Milin said he continued to press for contractors to be chosen on price rather than on their relationship with the union because PrimeSpace was under financial pressure.

Matters came to a head two weeks after a meeting in mid-July 2012 between Milin, PrimeSpace representatives and the real estate agents.

Mr Milin spoke about the impact the use of The Tradies' preferred contractors was having on the build price. "I also expressed some concern Milin had not been paid for some time," he said.

"On Sunday, July 29, 2012, I received a phone call from Anthony McDonald from PrimeSpace. He wanted to speak to me urgently. We met in Manuka at noon at the Public Bar.

"He [Mr McDonald] said: `I have some bad news. The Tradies have told me at 5.05pm on Friday that they will not proceed if Milin has any further involvement. They won't enter into the joint venture and they want Milin removed as the builder immediately. The only option is you kick in $5 million or I have to go with them'."

Mr McDonald said the CFMEU wanted to go with Construction Control as the builder.

Mr Milin said he finally got Mr Hall on the phone on the Tuesday or Wednesday to discuss the matter.

Mr Milin said: "He [Mr Hall] said `it is unfortunate, but we want to go with a builder we have a relationship with. We really want to make sure we are protected, we are nervous going into something like this."

The preliminary contract was terminated in August 2012.

The friction between Milins and the CFMEU is ongoing. Mr Milin told the commission that as recently as August 2014, Mr Hall told him the company would not be able to work on the $75 million Trilogy development in Woden without a union EBA.

Mr Milin said when he asked Mr Hall why he would not be able to work on the Woden apartment towers without an EBA Mr Hall said: "I'd be the laughing stock of the union movement in Canberra if we didn't have one in place. It's three 12-storey towers. It's just not going to happen [without an EBA]."

Mr Milin, who said he dictated a diary note of the conversation to a colleague two days later, asked Mr Hall if he was threatening him.

Mr Milin said Mr Hall replied: "Of course not, we don't do that, we don't threaten anyone."

Mr Hall is expected to respond to these and other allegations when he returns to give evidence during the last week of August.