The Fair Work Commission has found ACTION buses was right to fire one of its drivers, Peter Lambos, after he made the threat to a manager in December 2014, even though the prospect of a mass-casualty shooting at a Canberra bus depot was remote.

Mr Lambos, who had been driving ACTION buses since 2008, said he was raising health and safety concerns in a phone call to the network's health and safety boss Julie Mylchreest.

But Ms Mylchreest reported feeling shaken and sick to the stomach after the "disturbing" conversation, with Mr Lambos talking of "reprisals" for what he called the "despicable attitude of ACTION management".

"He refuses to take a backward step, threatened that if Action management touch me, this will be another Columbine'," Ms Mylchreest reported

Mr Lambos disputed the specifics of the conversation but did not deny referring to the 1999 massacre at Columbine High School in the United States that left 13 dead.

The driver was sacked after a psychiatric assessment provided no justification for his behaviour.

Part of his dismissal letter read: "I do not accept that a threat of violence is not a valid reason for termination, it was not for Ms Mylchreest, nor ACTION management, to know that you did not intend to carry out a shooting or violent act or that you did not have the means to carry out a shooting.

"We have a duty of care to ensure that all employees are protected and we take all threats and acts of violence seriously and do not condone such behaviour."

But Mr Lambos appealed his sacking to the FWC, arguing that ACTION should have known that he was never intending to open fire on his colleagues.

He told the commission he had used the word Columbine to make his point that the health and safety situation was escalating to dangerous levels and said he had a good work record with ACTION that should have been taken into account.

He also said the outburst to Ms Mylchreest had come against a background where he was the victim of workplace bullying, implied threats and "death stares".

But Fair Work Commission deputy president John Kovacic was not convinced, noting Mr Lambos had been given directions in the past from ACTION about "the importance of engaging with his colleagues in a respectful way, refraining from negative comments about colleagues and limiting his contact with managers to business hours".

Mr Kovacic found Mr Lambos' words about Columbine constituted a threat, which was reported to the police, and that his managers took the threat very seriously, although they did not believe they were likely to be shot.

"As to the genuineness of the threat, Mr Lambos' reference to "reprisals" in his conversation with Ms Mylchreest when allied with the reference to "Columbine" support a finding that Mr Lambos was making a threat of some form of action, albeit that it was unlikely to include a massacre," Mr Kovacic wrote in his decision.

The commission deputy president found Mr Lambos' sacking was not harsh, unjust or unreasonable and dismissed the former driver's claim.