Attorney-General Mark Dreyfus rebuffed calls to use special ministerial powers to end the case, saying they should only be used in "very unusual and exceptional circumstances".

The former Tax Office employee Richard Boyle will face a South Australian court on Tuesday to defend his actions, arguing they were consistent with the Public Interest Disclosure Act and therefore immune from prosecution.

Mr Boyle is facing a number of charges after he exposed debt collection tactics within the Australian Taxation Office to the media. If found guilty, he could spend life in prison for the alleged offences.

In a letter response to Greens senator David Shoebridge last month, Mr Dreyfus declined to discontinue the proceedings against the whistleblower, adding it required careful consideration.

Senator Shoebridge said the country's first law officer was "refusing to exercise" his powers against a "brave and principled" public servant in order to set an example for future whistleblowers.

"Richard Boyle's concerns have been vindicated by a Senate committee and two external reviews, the only purpose in continuing the case is to frighten other whistleblowers from coming forward," he told The Canberra Times.

"It was extraordinary that he was charged by the Morrison government in the first place and it is distressing to see the prosecution continue under Labor."

The case's timing coincides with the introduction of the proposed national anti-corruption commission model, for which Mr Dreyfus has vowed to protect "genuine" whistleblowers.

The Attorney-General outlined in his letter he was closely examining whistleblower reforms, including changes to the disclosure laws and the establishment of a whistleblower protection agency, but did not outline a timeline.

"Such reform options are complex and should not be rushed," Mr Dreyfus wrote.

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But the Greens senator said his use of the "exceptional circumstance" threshold was subjective, in reference to its inclusion in the recent integrity watchdog bill.

"It's hard to image a more exceptional case than that of Richard Boyle," Senator Shoebridge said.

"He is a brave and principled public servant who was shut down when he raised his concerns internally and only then took his concerns to the media.

"If Richard Boyle's case does not meet the test of 'exceptional circumstances' then heaven help anyone trying to get a public hearing in the new NACC [national anti-corruption commission] if the same test applies to that."

Mr Boyle is one of a number of high-profile whistleblowers who have been pursued by the Commonwealth in recent years.

The former public servant lodged a public interest disclosure in 2017 upon changes within the ATO forcing staff to use harsher debt collection tactics, including the use of orders that require a bank to hand over money from a personal or business account without the permission of the taxpayer.

He then took the information to the media after the disclosure was dismissed by the tax agency.

A parliamentary report released in 2020 found the ATO had conducted a "superficial investigation" into his concerns.

The Canberra Times sought a response from Mr Dreyfus but he declined to comment on matters on cases before the courts.

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