The operators of the Luas have failed to overturn an unfair dismissal finding against a driver sacked because he did unsanctioned extra work as a taxi-driver due to his wife developing a serious medical condition.
Transdev asked the High Court to overturn a Labour Court decision that Michael Caplis was unfairly dismissed and should be re-engaged.
Transdev claimed the Labour Court erred in law in its decision.
Mr Caplis, who worked as a Luas driver for 12 years until he was dismissed in August 2017, opposed Transdev's appeal.
On Tuesday, Mr Justice Richard Humphreys found Transdev had not raised a point of law which warranted the appeal and he dismissed the challenge.
The court heard a member of the public had complained to Transdev in April 2017 that he had seen Mr Caplis driving a taxi regularly on Friday and Saturday nights.
Luas drivers are not permitted other employment without the employer's permission because they are "safety critical workers" and their rosters are operated to mitigate against the risk of driver fatigue.
Transdev got a private investigator who filmed Mr Caplis driving a taxi and receiving fares on two days in May 2017.
A disciplinary process followed and he admitted he had been driving his wife's taxi in a very limited way from time to time in order to assist her following her diagnosis with a serious medical condition in February 2017.
He did not believe he was doing anything wrong and was only "backfilling" occasional hours at his wife's behest.
He was found to have committed gross misconduct, was suspended, and was ultimately dismissed.
He appealed and the Labour Court, last July, found the summary dismissal was not a reasonable response open to a reasonable employer in the circumstances of the case.
It said he admitted his conduct from the outset, offered an explanation with admittedly erroneous reasons for his belief that driving his wife's taxi from time to time did not equate to double jobbing.
The Labour Court also found it was not proven that there had been a breach of maximum working hours and rest provisions contained in the Organisation of Working Time Act 1997. It recommended his re-engagement.
In the appeal to the High Court, Marcus Dowling BL, for Transdev, argued Labour Court in its decision did not explain or record its reasons and as a result one had to engage in guesswork about what those reasons were. Its finding in relation to maximum working hours was "unbelievably wrong", counsel said.
There were "indisputable facts" about this case but the Labour Court decision did not look at them in the way, for instance, the High Court does, he said.
Peter Ward SC, for Mr Caplis, said his client was subjected to the full rigours of cross-examination before the Labour Court and also heard Transdev witnesses.
Transdev was "simply unhappy with the result" , he said.
They were operating a "zero tolerance policy" and while they said they did not do so, it amounted to that in dismissing him, counsel said.