The results of an online poll of 101 members of the Master Builders ACT members reported that 71.8 per cent of respondents had been verbally intimidated, and 41 per cent physically intimidated, by the ACT branch of the CFMEU on Canberra building sites.

But the CFMEU has branded the survey a "self-selecting, self-serving, online dribble fest" that did not represent the concerns of the wider industry.

CFMEU ACT secretary Dean Hall accused the MBA of ignoring the interests of honest companies and increasingly aligning itself with construction companies that engage in unlawful activity.

The results of the survey were released on Tuesday, as the Royal Commission into Trade Union Governance and Corruption prepares to sit in Canberra for three weeks of public hearings from next week.

Master Builders ACT executive director Kirk Coningham said the Royal Commission's impending presence in Canberra had given local builders confidence to speak about alleged CFMEU tactics of "intimidation and bullying that has become a sad fact of life on building sites in the territory".

"Previously they have only been prepared to talk about these issues in private for fear of reprisal," Mr Coningham said.

"We are now seeing fear being replaced with courage as construction workers reclaim control of their businesses and livelihoods in our city."

The survey also found that 58.4 per cent of respondents had received threats to exclude them from the market if they did not agree to pattern enterprise agreements, which requires payments to CFMEU associated entities.

About 32 per cent had been asked to make donations to the CFMEU or related business entities in exchange for 'industrial peace' and 7 per cent reported they had been asked for outright bribes.

"The central threat is that a company must meet the union demand or else they won't work in the commercial construction industry," Mr Coningham said.

"Those threats also prevent witnesses from coming forward – until now."

But ACT branch secretary Dean Hall argued the survey size meant it should not be treated as a snapshot of the Canberra construction industry.

He said the survey also received a number of comments complaining about payment issues and lack of law enforcement in the industry, which the MBA chose not to highlight.

Mr Hall questioned why the MBA had focused on the CFMEU when there were more pressing concerns in the ACT, including the worst safety record in the country, cases of workers being ripped off on superannuation, long service and other entitlements, and phoenixing and non-payment to sub-contractors.

"The ACT has been chosen as a battleground for the extreme right-wing industrial relations agenda of the national MBA and the Liberal Party," Mr Hall said.

"We don't want to see the honest, reputable builders and subbies go to the wall in the industry ... the CFMEU is campaigning for changes to the Corporations Act to stop the millions of dollars that are lost every year to businesses and workers alike.

"The MBA, on the other hand, has chosen to protect the interests of the big builders and developers. This encourages the activities of those phoenix companies which are breaking the law, and getting away with it at."

Mr Hall also asked why Canberra's peak construction industry group had last year vouched for the ACT CFMEU's integrity, only to now shift its position.

"It proves the lies and misrepresentation and the tarnishing of the union is solely about one thing, taking money out of workers' pockets and putting them in the hands of big business and developers.

"The CFMEU is proud of its history in defending workers' rights and will continue to do so."

The CFMEU ACT has recently come under sustained pressure with a federal government agency filing a number of lawsuits alleging it breached the Fair Work Act on a number of occasions.

One case alleges eight Canberra union officials blockaded a northside worksite and demanded the builder sign a CFMEU enterprise agreement.

While another alleges breaches of right of entry laws.

But Mr Hall has been defiant, saying the union would defend the allegations vigorously and "never walk away from a blue on safety".

Mr Hall alleged the Royal Commission and court cases are a political stunt by the Federal Government to erode workers' rights.

But Mr Coningham said the Royal Commission had nothing to do with safety or workers conditions.

"It has everything to do with challenging the criminal behaviours we have endured in our workplaces for far too long," Mr Coningham said.

"In hearings which it has already conducted in Melbourne, Sydney and Brisbane the Royal Commission has heard evidence of what the Royal Commissioner described as 'industrial blackmail and extortion'."