The same offence earlier cost the construction union and two of its stewards $78,000 in penalties.

Prolac Pty Ltd and its director Tim Petrusic were fined $16,200 after the construction sector watchdog took them to court for terminating the worker's contract in February 2017.

The company hired the worker to do some painting at the residential EQ Tower in Melbourne, though he was yet to pay his $1100 CFMMEU membership in full.

A few days into the job, a union shop steward at the site told the worker he was required to pay his outstanding fees.

The worker paid and was allowed to continue working at the site for the rest of the day, but the following day his contract was terminated.

"When I first engaged you, you know that you need to be a member of the union," Mr Petrusic told the worker.

"Whether I believe it or not, whether I give a f*** about it or not, I don't care, but that's rules that I've got to play by, in turn, you've got to play by, you knew that."

Australian Building and Construction Commissioner Stephen McBurney said it was unacceptable for an employer to sack a worker because they were not a union member.

"There is no place for 'closed shops' in Australian workplaces," he said on Monday.

When handing down the penalty in the Federal Court last week, Judge Michael Wheelahan described the contractor's actions as serious and deliberate.

"In my view, there was nothing inadvertent or accidental about what occurred," he said.

The CFMMEU and shop stewards Maurice Campanaro and Joe Caratozzolo were handed $78,000 in penalties in April after they were found to have coerced the subcontractor to pay his outstanding fees.

Australian Associated Press