The construction union has pledged to "vigorously fight" charges of cartel conduct laid against it by the corporate watchdog.
The Australian Competition and Consumer Commission alleges the union attempted to induce the territory's steelfixing and scaffolding businesses to engage in cartel conduct.
On Thursday, the watchdog revealed it had laid charges against the ACT branch of the Construction, Forestry, Maritime, Mining and Energy Union and its secretary Jason O’Mara.
ACCC Chair Rod Sims said the union and Mr O'Mara are each accused of attempting to "induce suppliers of steelfixing services and scaffolding services to reach cartel contracts, arrangements or understandings containing cartel provisions in relation to services provided to builders in the ACT in 2012 to 2013".
Cartel conduct is when businesses agree to collude instead of compete against each other.
Steelfixing is the installation and fixing of reinforcement steel on building sites, including in concrete slabs.
Scaffolding services include the erection and dismantling of scaffolding on building sites.
However, CFMEU national construction secretary Dave Noonan said the union denied it had committed any breaches of consumer and competition laws.
“The union’s role is to negotiate wages and conditions for workers in the industry. We intend to continue to do our job while vigorously defending our position," Mr Noonan said.
"We note that other criminal procedings out of the royal commission, Setka, Reardon, and Lomax, all collapsed and we're confident of successfully defending this matter.
"In each of these cases, there's a common thread, all the official has been accused of is negotiating better wages and conditions for construction workers, consumers must be wondering why the ACCC spends its time chasing unions rather than addressing the big rip-offs at the petrol pump."
Mr Sims said the charges followed a joint investigation between the corporate watchdog and Federal Police following the Royal Commission into Trade Union Governance and Corruption.
The ACCC declined to comment further as the matter was now before the court.
In 2015, the Canberra hearings of the Royal Commission into Trade Union Governance and Corruption heard allegations of price fixing in the Canberra construction industry.
Counsel assisting the royal commission, Jeremy Stoljar, SC, raised allegations of price fixing and that cartels for key trades may have been formed as a result of the CFMEU's alleged pattern bargaining practices.
The corporate watchdog immediately announced it would prove the allegations.
The matter will appear before the ACT Magistrates Court in September.
The ACCC recently ramped up its efforts to gather more information on cartel conduct by putting in place a number of measures to enable potential whistleblowers to come forward anonymously.
The ACCC’s anonymous reporting portal allows members of the public to report and communicate anonymously with investigators about anti-competitive practices in the construction sector.