The Australian Taxation Office has warned staff to follow the rules on accessing tax records or face losing the job in a move a union described as unfair and motivated by political pressure.

Tax commissioner Chris Jordan told staff in a message last Tuesday an agency review found more than 30 employees had accessed taxpayer data without proper authorisation, resulting in being sacked or forced to resign.

He conceded not all had been for nefarious reasons but the agency needed to take a zero-tolerance approach in order to maintain public confidence.

"The community trusts us with their personal information and has confidence that we will use it for the purposes they have provided it to us," Mr Jordan said.

"I say it a lot, but it's worth repeating: we need taxpayers to have this trust in us in order to do our jobs."

The tax office would not provide additional figures for previous years to The Canberra Times, or a specific time period for the dismissals, but said the unauthorised access attempts were infrequent.

"The ATO takes secrecy of taxpayer information very seriously," a spokesperson said.

"The ATO has a zero-tolerance approach to breaches of secrecy obligations and utilises rigorous detection methods to identify accesses that may be unauthorised.

"Our approach continues to evolve with the use of emerging technology. Cases of unauthorised access happen infrequently, and when they do the ATO acts swiftly to take appropriate action."

The agency added firing staff was one way it dealt with staff that breached the policies but other sanctions could include fines or reductions in classification.

In serious cases, terminated employees could also be referred for consideration of criminal investigation or prosecution.

According to the agency's previous annual reports, an average of nearly 30 staff had been dismissed each year in total since the 2016-17 financial year, with an average of more than 350 resignations during that same period.

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The Australian Services Union said not all examples of unauthorised breaches had been malicious.

The union pointed to one example where a member had accessed a record of her family's superannuation fund, of which she was a trustee, in order to pay a tax debt.

She was allegedly suspended without pay for seven weeks before being terminated from the role.

Tax branch secretary Jeff Lapidos said the tax office had taken a tough stance in response to being strong-armed by politicians but was disregarding breaches stemming from goodwill or misunderstanding.

"Termination of employment should be reserved for the most serious cases of misconduct and not the least serious, as occurred here," Mr Lapidos said.

"The ATO has responded to parliamentary criticism by scapegoating everyone who made an unauthorised access.

"The ATO makes it more difficult for staff to get information about their own tax affairs than the general public. This is part of the problem, which needs to be addressed."

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