Media reports of the alleged assault came on the same day as the royal commission into trade union governance and corruption heard claims of widespread extortion by the CFMEU against companies around the country.

Senator Abetz said reports that Fair Work Building and Construction staff had been physically and verbally assaulted on the Barangaroo site "are a cause of great alarm”.

A NSW Police spokesman said an incident had been reported to police and inquiries were continuing. No charges had been laid.

The national secretary of the CFMEU, Dave Noonan, said the union and the official accused of assault last month had not been contacted by police. He accused the federal government and Fair Work Building and Construction of colluding to smear the union by leaking details of the alleged assault to the media.

Fair Work Building and Construction director Nigel Hadgkiss said: "It is of concern to me that this kind of behaviour towards government officials appears to be increasing around the countryside."

Senator Abetz said allegations of a male official being shoulder charged and the verbal abuse of a female officer on the Lend Lease site confirmed the need to restore the Australian Building and Construction Commission, which the former Labor government had abolished. The Coalition introduced Fair Work Building and Construction to replace the commission.

“It is not a radical concept, but seemingly some CFMEU officials cannot comprehend that bullying, intimidation and violence have no place in society and just because you are a union official does not make you above the law,” Senator Abetz said.

“For Commonwealth officers, including female staff, to be verbally and physically assaulted is not only a breach of Commonwealth law but also a breach of the standard in which society expects all Australians to abide.”

Mr Noonan dismissed Senator Abetz' comments as "another dishonest smear" in a campaign to return to the Howard government's Work Choices legislation.

"As a lawyer, Senator Abetz knows the [Australian Building and Construction Commission] could not prosecute criminal behaviour. The allegation is one of assault and would have to be prosecuted by the police. Another example of lies and misinformation to return to Work Choices," Mr Noonan said.

At the royal commission hearing in Brisbane, the CFMEU's counsel John Agius, SC, challenged allegations of extortion and misuse of workers' contributions to the union's welfare, redundancy and income protection funds.

"It just shows that when witnesses are subject to cross-examination the lurid statements by the counsel assisting are not supported by evidence," Mr Noonan said.

Counsel assisting the royal commission, Jeremy Stoljar, alleged that companies including Universal Cranes had been banned from building sites in Brisbane for refusing to enter enterprise bargaining agreements with the CFMEU.

Mr Stoljar said the CFMEU, which received payments of more than $3.3 million in the financial year ending June 30 through contributions to the redundancy fund and other schemes, had not paid interest earned to employees.

Mr Stoljar alleged payments made as training grants were used to meet CFMEU expenses instead of delivering training.

He said evidence by Albert Smith, the director of Universal Cranes, if accepted, demonstrated CFMEU officials' "willingness to commit serious crimes and engage in other unlawful conduct in an attempt to strengthen the union's position" through industry funds.

The union has been accused of telling contractors not to use Universal Cranes on work sites from 2012 and of coercing Universal Cranes to not exercise its workplace rights.

"If Mr Smith's evidence is accepted, questions arise as to whether officers of the CFMEU have engaged in a deliberate and protracted criminal campaign of extortion against Universal Cranes," Mr Stoljar said.