The Fair Work Commission has found the ATO's sacking of an IT technician who accessed ''unacceptable material'' featuring bestiality on his work computer was neither harsh, unjust or unreasonable.

The commission found that Thanh Vu had been warned in the past about inappropriate use of the ATO's computers and was well aware of the consequences of another breach when he stored the offending material.

The decision follows a case last year where the Defence Department's sacking of a civilian contractor for internet ''smut'' was upheld by the tribunal, but the government was forced to pay the man a five-figure compensation settlement after the bungled dismissal denied him procedural fairness.

Mr Vu was sacked by the ATO in August after being investigated for a breach of the Australian Public Service code of conduct.

His bosses' suspicions were aroused in May that year after a routine sweep of the technician's emails revealed he had forwarded, to his home account, material known as the ''corpse email'', which the commission found inferred cannibalism.

Further checks of Mr Vu's computer uncovered more material, some of it portraying sexual activity between a woman and a tiger, including the genitals of both and sexually explicit prose in Vietnamese. Mr Vu took his sacking to the Fair Work Commission arguing that the punishment was disproportionate to the crime, that he would lose up to $400,000 in superannuation benefits, and that he was married with four children and unlikely to get another job.

But in its defence, the ATO wheeled out some senior executives to give evidence including one of its human resources bosses David Miller who said he did not accept the department's employees could be unaware of its ''zero tolerance'' approach internet porn.

''I consider it implausible for any employee, and in particular any employee in the IT area of the ATO, not to know of the policy on the use of IT facilities and updates on that policy, how it is enforced, and the consequences of breaches of the policy,'' Mr Miller said in his evidence.

Most damaging to Mr Vu's case was a ''reminder notice'' his bosses sent him in 2010 relating to a ''cartoon image containing crude content'' sent by the technician to an external email address in October that year.

Fair Work Commissioner Barbara Deegan found Mr Vu knew the seriousness of his conduct when he forwarded the images last year.

''All the evidence supports a view that he knew his conduct was in breach but, nevertheless, engaged in the conduct,'' the commissioner wrote in her judgment.

Nor was she moved by Mr Vu's evidence that he had been dealt with too harshly by his former bosses.

''I accept that the applicant will suffer as a result of the dismissal,'' Commissioner Deegan wrote.

''I do not however, accept that the effect of the dismissal on him is such that it renders the termination, in all the circumstances of this case, harsh.

''All employees who lose their jobs suffer to differing degrees.

''Many don't have superannuation benefits at the levels enjoyed by public servants.''

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