A Federal Circuit Court judge found Elias Taleb and his company Class 1 Form underpaid the employee $16,366.

In a judgement, published in December, Judge Warwick Neville fined the formwork company $30,000 and ordered it compensate the worker the unpaid wages.

Mr Taleb's explosive evidence, delivered on the first day of hearings in 2015, exposed dodgy practices in parts of Canberra's construction industry.

He detailed payments to a Construction Forestry Mining and Energy Union ACT organiser, which led to high-profile arrests and criminal convictions.

The fallout of the royal commission is still being played out in the ACT's courtrooms.

Mr Taleb had described to Commissioner Dyson Heydon how he paid $70,000 in bribes to former construction union official Halafihi Kimonu Kivalu to guarantee he would win contracts in Canberra.

He claimed Kivalu had blackmailed him over work at a Yarralumla residential development between February 2012 and June 2013, and an apartment complex development in Braddon between September 2013 and January 2014.

Mr Taleb believed the construction union would disrupt work at his sites if he did not pay.

Kivalu's racket, which preyed on hard-working businesses, was taken down on the basis of Mr Taleb's testimony after investigators used it to convict him of criminal charges.

Kivalu pleaded guilty to blackmailing Mr Taleb and was last year handed a suspended jail term of two years and nine months.

He was also ordered to pay Mr Taleb reparations of $70,000.

But Mr Taleb's own dodgy workplace methods became the target of legal action when the CFMEU and former Class 1 Form worker last year launched the civil case against him and his company.

The casual employee said he had been underpaid for about six months of carpentry work in 2013 and 2014.

He said the business had paid him $35.40 an hour, when he was entitled under his agreement to receive $35.80, and later $37.59 per hour.

The worker claimed the business failed to pay his casual loading of 25 per cent, which also meant he was not paid correct superannuation.

He had been entitled to a travel allowance of $35.11 and then $36.87 per day, but only received $33.44.

There were several occasions when he was not paid on time.

Judge Neville found the company and Mr Taleb breached their agreement under the Fair Work Act by failing to pay the worker correct wages, casual loading, travel allowance, and superannuation.

The judge wrote the worker suffered "serious loss" in the three-year delay since the breaches first occurred and the fact he had been denied basic entitlements was warranted firm intervention by the court.

He found the breaches were serious but characterised the offences at the lower end of the scale.

While the amount owed to the worker may have appeared "relatively modest", he noted "a small amount to one may be a large amount to another".

The court accepted that there had been no evidence of previous proceedings against the company or Mr Taleb.

But Judge Neville found the respondents had not shown contrition or remorse, or sought to take corrective action.

"In fact, the respondents have refused to participate in the proceedings although on various occasions have suggested that they would."

He took into account their submission all penalties would "come from the same pocket" given the company was a single shareholder business managed by Mr Taleb.

Judge Neville fined Class 1 Form $18,000 and Mr Taleb $12,000. Those penalties would be paid to the CFMEU.

"The denial of entitlements to an employee is a serious matter," the judge wrote.

"I also accept that it has taken a number of years for the matter to be determined.

"[The worker] was a skilled employee; the respondents benefited from those skills but did not honour the relevant payments due to him under the collective agreement."