It is the first time Mr Lomax, an ACT-based organiser with the construction union, has been found to have breached any industrial law, something which the Federal Court of Australia found was to his credit.

But the court lashed out at the CFMEU, and said it had a "dismal" record of complying with industrial legislation.

Federal Court Justice Richard White found it was "probable" that the union deliberately brought in officials from interstate to walk onto the South Australian worksites unannounced.

"Even if that not be the case, it is evident that the CFMEU chose in a premeditated way to have several officials engage in the unlawful conduct at each site, and for that purpose, bolstered the numbers of its South Australian based organisers with those from interstate," he said.

Mr Lomax was one of four union officials who walked onto a construction site at Flinders University without notice in October 2013.

The site was being managed by property group Lend Lease, and the site manager challenged the group.

One of the union officials, Mark Gava, responded with words to the effect of:

"We are not leaving. This is the way it's done now. We're going for a walk on the site."

The union officials walked around the site, talking with workers, and then Mr Gava threatened to cause work to be stopped unless the CFMEU flag was flown from a crane.

They remained on the site for roughly an hour and 40 minutes.

Mr Lomax was not found to have coerced the site manager himself in any way, but was said to have been "present when coercive conduct occurred".

"[He] did not disassociate himself from any of the statements made by his colleagues, and accompanied the CFMEU officials onto the site," Justice White said.

Justice White said the CFMEU must have intended to have placed four officials on the site to "make its point more forcefully to Lend Lease".

"In other words, the CFMEU intended that there be multiple contraventions and sought by doing so to pursue its own purposes," he said.

Mr Lomax was personally fined $3000 for two contraventions, while his actions saw the CFMEU fined a further $50,000.

The case also involved contraventions by other CFMEU officials at a further three sites, all of which attracted significant fines.

In a judgment published last week, Justice White attacked the CFMEU's record on breaching industrial legislation.

He said that between December 2000 and October 2013, the CFMEU and its officials were dealt with by the courts on 80 separate occasions for contravening industrial legislation.

"On any reasonable measure that is an appalling record," he said.

"It bespeaks an attitude by the CFMEU of ignoring, if not defying, the law and a willingness to contravene it as and when it chooses."

"This means that specific deterrence in particular must be a prominent consideration in the penalties imposed on the CFMEU in the present case."

The fine comes roughly eight months after ACT prosecutors dropped allegations of blackmail against Mr Lomax in Canberra courts, after accusing him of forcing a Canberra painting company and its principal to sign a union enterprise bargaining agreement.

The charge, one of the most high-profile to stem from the royal commission into union corruption, was dropped in October.