Public Service Commissioner Gordon de Brouwer's opening statement to a Senate estimates committee on Monday said the commission was still conducting "around two dozen investigations" into the behaviour of public servants.

This number remains unchanged from the October estimates.

These code of conduct inquiries include 15 investigations into public servants in relation to their involvement in the unlawful robodebt scheme.

The commission last week announced that four of these public servants have been given a "preliminary determination" that they breached the code, while 11 investigations remain ongoing.

Dr de Brouwer noted that a code of conduct inquiry is not a public civil or criminal investigation, and said this was the basis for the heightened secrecy around such probes.

"Because it occurs legally within the employment relationship and is subject to privacy law, the starting point is that it is confidential and constructive," his statement reads.

"I understand public commentary questioning the level of secrecy around code of conduct investigations and the time that they can take."

But public disclosure can be made where the commissioner "is satisfied that it is in the public interest and disclosure of a person's name is fair and reasonable", he said, adding that this was the case for Mr Pezzullo's inquiry.

Home Affairs Minister Clare O'Neil referred Mr Pezzullo to the Public Service Commission in September 2023, after Nine published allegations he had sought to wield political influence, over the course of hundreds of text messages with a Liberal powerbroker.

Dr de Brouwer appointed former Public Service Commissioner Lynelle Briggs to lead the inquiry, which found Mr Pezzullo had breached the APS code of conduct on at least 14 occasions in relation to five overarching allegations, including using his duty, power, status or authority to seek to gain a benefit or advantage for himself.

He was sacked in November 2023, following recommendation from the inquiry.

"This high threshold was met in the circumstances surrounding the code of conduct investigation into Mr Pezzullo," Dr de Brouwer said in his statement.

"The release of high-level findings sought to balance the public interest in this matter and the importance of maintaining the integrity of statutory processes."

The commission released a statement on the findings of the inquiry, but not a full report.

"I welcome public scrutiny," Dr de Brouwer stated.

"The Commission works hard to conduct investigations properly in accord with all the dimensions of the law and the public's expectations of accountability for the service's actions."