The nation's top public servant has rebuked the chairman of the National Broadband Network for writing an opinion piece during the election campaign.

Key points: NBN chairman wrote opinion piece supporting police raid on Labor senator's office

NBN chairman wrote opinion piece supporting police raid on Labor senator's office Head of the public service says this breached caretaker government conventions

Head of the public service says this breached caretaker government conventions NBN says piece needed to challenge 'misleading claims'

The Federal Opposition complained about the piece, published by Ziggy Switkowski, following police raids on the offices of a Labor Senator in May.

In response, a letter from Martin Parkinson, the head of the Department of Prime Minister and Cabinet (DPMC), said the column was "not consistent" with the Government's caretaker conventions.

He said Dr Switkowski was also warned by the DPMC before the piece was published.

"The Department of Communications and the Arts sought, and received, advice from the Department of the Prime Minister and Cabinet that the publication of the article in that form was not consistent with the established practices associated with the Caretaker Conventions," Dr Parkinson said.

"I understand that view was strongly conveyed to NBN by the Department of Communications and the Arts, as was the view that the conventions apply to the Chairman, as well as to the CEO and the company."

The opinion piece by Dr Switkowski, published on May 28, said he made "no apologies" for the police raids on the offices of Labor Senator Stephen Conroy, an outspoken critic of NBN, over the leaking of sensitive internal documents.

"When dozens of confidential company documents are stolen, this is theft," Dr Switkowski wrote.

"When they are the basis of media headlines and partisan attacks, they wrongly tarnish our reputation, demoralise our workforce, distract the executive, and raise doubts where there is little basis for concern.

"The process is a form of political rumourtrage — the circulation of misinformation to diminish an enterprise for political gain."

Opinion piece challenged inaccurate comments: NBN

In a statement released today, NBN defended Dr Switkowski's opinion piece, which it said "addressed misleading claims to restore the trust of its 5,000 employees".

"Inaccurate comments that accuse the company of deliberately misleading, deliberately concealing, and then persecuting innocent whistle-blowers have a tremendously corrosive effect on morale and jeopardise the great gains made over the last few years," the statement said.

"The opinion piece addressed the allegations in a manner commensurate with the mode in which they were made; that is, publicly in the national media."

In the letter Dr Parkinson noted while the caretaker conventions do not have "legal force", the maintenance of the apolitical and impartial nature of the public service "is a matter of the highest priority for me as head of the public service".

A spokeswoman for the DPMC declined to comment further.

PM must take action over breach: Shorten

Opposition Leader Bill Shorten said Prime Minister Malcolm Turnbull needed to "show leadership", describing the matter as a "flagrant breach of caretaker conventions".

"On one hand if he doesn't sack Dr Switkowski or take action, he's condoning a breach of caretaker conventions," Mr Shorten said.

"And of course if he does, it sort of confirms that the game is up in terms of how NBN has really been going in the last three years."

A spokesman for the Coalition defended Dr Switkowski, describing him as "an independent chair, on his own judgement and also one not unfamiliar with the (caretaker) convention".

The spokesman accused the former Rudd Government of breaking caretaker conventions in 2013.

"We are not going to take lectures from the Labor Party which ran taxpayer-funded advertising during the 2013 election campaign in clear breach of the conventions and contrary to the advice of officials — at a cost $6.5 million to the taxpayer," he said.