A Perth couple has been awarded more than $720,000 in compensation for being refused jobs because they were not union members.

The Federal Court ordered Offshore Marine Services (OMS), now called Skilled Offshore, and the Maritime Union of Australia (MUA) to pay the couple more than $350,000 each.

Bruce and Lynne Love were promised offshore jobs as a steward and a cleaner with OMS in 2009 with combined wages of $220,000 providing they completed training and joined the MUA.

However, the couple in their 50s were denied membership twice before the jobs were given to existing union members.

The Fair Work Ombudsman took legal action against both OMS and the MUA in June 2011.

In May 2012, OMS was fined $7,500 by the Federal Court after admitting its role, but the MUA denied liability and defended the allegations.

Justice John Gilmore ruled the MUA breached the Workplace Relations Act by bullying the hire firm not to employ the couple.

The judge said that the MUA's conduct "involved its blatant use of illegitimate industrial action power to bully OMS" into refusing to employ the couple.

Under workplace laws it is unlawful for an employer to refuse to employ a person based on whether the person is a member of a union.

Justice Gilmour also found that the MUA's actions deprived the couple of the opportunity to gain well-paid employment "at a critical time of their lives", and that OMS "succumbed" to union threats of industrial action, even though it wanted to employ the couple.

He noted that "engaging in conduct with an intention to enforce a closed shop" on the West Australian waterfront was "objectively serious".

"The penalties must be sufficient to deter the MUA from engaging in further unlawful conduct of this type," he said.

The MUA was also fined more than $79,000.

The union has been contacted for comment.

'Closed shop' totally unacceptable: Fair Work

The Fair Work Ombudsman's director of legal practices, Mark Davidson, said the court was clear in its message.

"I think it sends a very strong message in respect of this type of behaviour that only employing somebody because they are a member of a union is not acceptable," he said.

"Enforcing a closed shop is totally unacceptable in today's workplace environment."

He said he was not surprised by the extent of the compensation.

"The compensation that we saw was to cover Mr and Mrs Love for lost wages over a period of five years for Mrs Love and six years for Mr Love," he said.

"I would imagine that they would be satisfied that they have received compensation for what they would've otherwise received in that period of time."

Fair Work Ombudsman Natalie James agreed the court's decision sent a strong message.

"Employees have the right to join or not join a union and this should not have any bearing on their ability to seek paid employment," she said.