The Australian Taxation Office was shabby, appalling, disgraceful, unconscionable and dishonest in its treatment of one of its public servants who was recovering from a mental illness, according to Fair Work Australia.

And the workplace umpire has accused the ATO of wasting thousands of dollars of taxpayers’ money by flooding a commission hearing with highly paid lawyers to defend the illegal lock-out of the employee.

The ATO said on Monday it was reviewing the case but would not answer questions about its conduct towards public servant Brett McAuliffe, citing privacy rules.

Fair Work Australia Commissioner Bernie Riordan said he was appalled at the conduct of taxation managers in Sydney who posted a photograph of the public servant at the security desk of his office and told guards not to let him into his workplace, despite Mr McAuliffe being medically certified to return to work.

Mr McAuliffe had been diagnosed with adjustment disorder  after alleging he was bullied by his bosses but had been cleared by a psychiatrist to return to work by August 2013.

But Mr Riordan found that Mr McAuliffe’s managers did not want him back and turned to underhanded stalling tactics to keep him away from work, despite being aware he was in financial strife.

According to the Fair Work Australia decision, ATO manager Jenny Giang sent Mr McAuliffe home from work on August 11, 2013, “for reasons which defy any credible explanation”.

Commissioner Riordan found Ms Giang went on to deliberately misrepresent the opinion of psychiatrist Howe Synnott, mislead the employee, exceed her authority, ignore ATO policy and “deliberately and mischievously delayed Mr McAuliffe’s return for another seven weeks”.

Among the ATO's stalling tactics that Fair Work Australia found was an approach to Dr Synnott’s boss.

“Contacting Dr Synnott’s supervisor to seek clarification was a disgraceful attempt to interfere with the independence and professionalism of Dr Synnott, by wielding the weight of the patronage of the ATO in that practice,” Commissioner Riordan wrote.

“Ms Giang did not act expeditiously, responsibly or honestly.”

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Mr McAuliffe’s unfair dismissal claim had to be dismissed by Fair Work because he had not actually been sacked but Commissioner Riordan agreed that it was understandable the taxation worker would think he had been fired.

The commissioner wrote that he expected better from a large public sector employer and recommended Mr McAuliffe be paid his lost wages.

“At a time when Australian society is focusing on the issues of mental health in the workplace, the actions of the ATO in this case were unconscionable,” Commissioner Riordan wrote.

“I sincerely hope that an employee diagnosed with depression and anxiety in the future is not treated in the same shabby manner as Mr McAuliffe.”

The commissioner also let fly at the Taxation Office for bringing seven lawyers to a hearing, including a partner in global law firm Norton Rose Fulbright and Sydney barrister Bryce Cross.

Mr Cross had been denied permission by Fair Work Australia's full bench to appear for the ATO but the barrister showed up anyway, took notes throughout the hearing and actively assisted the conduct of the government’s case.

“This can hardly be an appropriate expenditure of public money,” the commissioner wrote.

“The policy of the Commonwealth in refusing to consider conciliation in this proceeding was disappointing.

“This should be the subject of review.”

 An ATO spokeswoman said the office was “considering” Commissioner Riordan’s decision.

“We will review the case and our work practices to improve our processes where appropriate,” the spokeswoman said.