Construction unionist Joe McDonald held a worker by the neck and raised a fist at him in a bid to get him to join an unlawful strike, according to court documents.
Mr McDonald threatened hydraulics worker Eddie Ierace in March last year to stop him entering the Mundaring Water Treatment plant on the third day of a stoppage.
The threat was at one of several strikes at two Brookfield Multiplex sites last year that this week cost the union $500,000 in compensation and about $200,000 in penalties.
The amount, which excludes legal fees, is equivalent to annual membership fees for almost 1000 workers.
Federal Court documents say Mr McDonald, the assistant secretary of the Construction, Forestry, Mining and Energy Union, incited and encouraged plant workers to strike after a site worker lost control of a water cart that came to rest in a ditch.
About 150 workers employed by contractors downed tools after Mr McDonald called for action at a March 25 meeting.
But when employees with hydraulics company Hexagon tried to return to work, Mr McDonald warned there would be "world war three" if they did not join the strike and they would not work on a unionised site again.
"We'll come through and do an audit, give you a hard time, we'll picket all your jobs, we'll get you thrown off every construction site you're on in Perth," Mr McDonald told the workers.
"If you go in there, it'll be the end of your company."
On the third day of the strike, Mr Ierace sought to push past Mr McDonald to enter the site.
"Mr McDonald physically held Ierace by the neck and raised his fist at Ierace in a threatening way," the court document says.
The union was ordered to pay $250,000 compensation for action at the water plant and the same amount for strikes at Fiona Stanley Hospital in February last year. Up to $200,000 is payable in penalties and Mr McDonald was banned from entering any Multiplex site until 2017.
Two other officials were penalised for their actions.
Kim Richardson from the Master Builders Association accused Mr McDonald of bullying.
"They rightly say bullying behaviour at the workplace has no place but condone their assistant union secretary bullying a construction worker who did not want to go on strike," he said.
CFMEU secretary Mick Buchan refused to condemn Mr McDonald's behaviour.
"He's been elected by the officials for 25 years and he does a very good job," he said.