Allegations of intimidation will be put to senior ACT Construction, Forestry, Mining and Energy Union (CFMEU) officials today, as they appear at the Royal Commission into Trade Union Governance and Corruption in Sydney.

Three days of hearings have been set aside to interrogate ACT branch secretary Dean Hall and union organiser John Lomax about the claims made by Canberra builders in July.

Earlier this year, three weeks of hearings in Canberra revealed allegations of a hidden culture of violence and a coercive internal culture within the construction union's local operations.

The claims ranged from coercing contractors to sign union-drafted enterprise bargaining agreements (EBA's), to worksite intimidation if builders did not comply with demands.

There were three arrests on the sidelines of the commission hearings in Canberra.

Last week, the Australian Federal Police dropped blackmail charges against Mr Lomax.

Some builders alleged Mr Hall and Mr Lomax were two of the officials who would carry out disruptive activities on worksites if they did not get their way during industrial negotiations.

A Canberra policeman had given evidence that Mr Lomax tried to intimidate him at a building site after he went there to investigate reports CFMEU officials were trespassing.

Former union organiser Fihi Kivalu is facing two counts of blackmail after evidence at the commission claimed he demanded tens of thousands of dollars in bribes from builders to give them access to the local construction market.

A third man, Tuungafasi Manase, who was an acquaintance of Kivalu, was also arrested for allegedly giving misleading evidence to the commission.

Police also executed a search warrant on the Dickson headquarters of the CFMEU in August, seizing files and computer hard drives.

The CFMEU has been highly critical of the investigations into its ACT operations, saying its officials have always had the interests of their members at heart.

The union has highlighted the poor safety record of Canberra building sites, and the appearance of its officials on worksites to investigate safety concerns is indicative that culture persists.

Senior officials have also claimed that allegations of coercion stem from builders trying to blame others for their own mismanagement.