The competition watchdog has launched raids on the CFMEU's Canberra headquarters as part of an investigation linked to allegations of price fixing in the construction industry.
CFMEU ACT branch secretary Dean Hall said more than a dozen Australian Competition and Consumer Commission officials and several Australian Federal Police officers arrived at the union's Dickson offices about 8.30am.
Mr Hall said the search warrant indicated the ACCC was searching for evidence of cartel conduct, or price fixing, within the ACT construction industry and stemmed from allegations made at the trade union royal commission.
"The CFMEU has never been involved, and will never be involved, in how bosses decide to sell their goods and services," he said.
"We're very proud of the fact we negotiate to get the best possible pay and conditions for workers."
The ACCC confirmed it was executing search warrants in the ACT and surrounds on Tuesday. It would not comment on which other premises it targeted.
"As this action is part of an ongoing investigation, it is not appropriate to comment further at this time," a spokeswoman said.
Mr Hall said the raid was an "extraordinary waste" of taxpayer money and resources.
He said the ACCC workers had been collecting electronic and hard copies of documents and expected they would remain at the premises into the night. The federal police left earlier in the morning.
MPR Scaffolding director Petar Josifoski gave evidence at the royal commission that the CFMEU allegedly told a meeting of scaffolders it was trying to get companies to agree to a minimum price for jobs.
Mr Josifoski claimed he told the meeting that the suggestion was price fixing and they could be jailed for discussing it.
The CFMEU said in a statement on Tuesday night it was co-operating with the probe and officials were seeking documents related to the Competition and Consumer Act linked to a case study conducted by the royal commission.
The union rejected any allegation it had breached the act.
"It should be noted that the royal commission was unable to conclude that the CFMEU had breached the Competition and Consumer Act," the statement said.
"The union makes no apology for negotiating enterprise bargaining agreements for its members under the Fair Work Act."
The statement said the CFMEU would defend the rights of construction workers to bargain for wages and conditions, and condemned the federal government's use of the ACCC to undermine those rights.
The AFP was ordered last year to return most of the thousands of documents seized during a raid on the CFMEU's Canberra headquarters in August.
ACT Supreme Court Justice Richard Refshauge found in December that part of the search of the Dickson offices had been unlawful and ruled police withheld information from the magistrate in order to get the warrant.