APS staff uphold impartiality. They expect it of their leaders too.

They'll go quiet in chats if talk veers towards anything that could be seen to be an opinion on their work.

It's a concept drilled into young graduates, and cautiously maintained throughout their careers. There are harsh consequences for those judged to have veered over the line, ranging from reprimands, to demotions or termination.

And though officials are allowed to act in private capacities, the spectre of those punishments often necessitates degrees of caution in their daily lives too.

It can dictate what they post online, how they engage with protests and campaigns - including the Voice to Parliament referendum - or even what they say over the dinner table.

Public servants are not just bound to this value by the APS Code of Conduct, but for most, by a sense of duty to taxpayers.

A duty to be part of a system which acts in the best interests of Australians, beyond the reach of political influence.

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For these reasons, allegations that one of the federal public sector's most senior leaders has not acted with the same sense of duty will be bitterly received.

Reporting by the Nine newspapers alleged Home Affairs secretary Mike Pezzullo had sent thousands of text messages to a Liberal source over a span of years, in which he is alleged to have sought to wield influence over political appointments.

Mr Pezzullo stood aside from the position as the Australian Public Service Commission commenced an inquiry into the allegations, led by former Public Service Commissioner Lynelle Briggs.

The Prime Minister is confident this will be done "in an expeditious way", but in the meantime, those at the APS ranks are left to mull over another potential instance of senior leadership dropping the ball.

The allegations land in the same year that robodebt Royal Commissioner Catherine Holmes released findings into the unlawful scheme, including evidence of APS leaders being "excessively responsive to government, undermining concept of impartiality and frank and fearless advice".

Robodebt exposed a system in which some of the loudest voices came from the bottom, as junior and mid-level public servants urged leaders to take action to end the flawed program. Despite their best efforts, a number of former public servants told the royal commission their concerns were drowned out, allowing a scheme now considered "neither fair nor legal" to run on for years.

Just weeks ago, public servants at the agency which administered the scheme received an apology for the "unfair toll" it had on them. In a wide-ranging apology, retiring chief executive officer Rebecca Skinner recognised that it was Services Australia staff, many of them who had nothing to do with robodebt, left facing questions about the state of the agency.

And once again, public servants will face questions over the actions of those at the very top.

It will be crucial for the APS Commission to execute this investigation in an effective and efficient way.

While senior APS leaders have acknowledged a need to regain public trust, they are just beginning to realise the breadth of work to be done in their own departments.

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