Last month the co-chair of News Corp filed defamation proceedings against Crikey over a June 29 opinion piece by politics editor Bernard Keane regarding hearings into former US president Donald Trump and the Capitol riots in Washington, DC, on January 6, 2021.

According to court documents, the article was defamatory by falsely claiming Mr Murdoch entered an illegal criminal conspiracy with Mr Trump to overturn the US 2020 presidential election and incite a mob with murderous intent to march on the Capitol.

The article, "Trump is a confirmed unhinged traitor. And Murdoch is his unindicted co-conspirator", twice mentioned the Murdoch family name.

Under the public interest test, Mr Murdoch must show the article "caused, or is likely to cause, serious harm" to his reputation.

Crikey must prove it reasonably believed that the publication of the matter was in the public interest.

Private Media CEO boss Will Hayward on Thursday said the right to express such an opinion was "absolutely critical" to the functioning of an open, modern democracy.

"We stand firmly against censorship, especially in matters of significant public interest," Mr Hayward said.

"As such, our case will test the new 'public interest' defence, specifically as it relates to opinion writing, as opposed to investigative reporting."

Private Media will also argue the article did not cause serious harm to Mr Murdoch.

"We think it is important in an open, well-functioning society that the rich and powerful can be critiqued, and that there is a high bar to reach before they have suffered serious harm from an opinion article," Mr Hayward said.

"We do not believe that the average Australian of reasonable intelligence (the test for this part of defamation laws) would have read our article and interpreted it in the way Mr Murdoch claims."

Mr Murdoch, who has retained high-profile defamation barrister Sue Chrysanthou, SC, in the lawsuit, is seeking aggravated damages.

Crikey has since written numerous other articles on Mr Murdoch, the events of January 6, 2021, and the then looming legal action, openly publishing all letters sent between the Fox CEO's lawyer John Churchill and Private Media's solicitors at MinterEllison.

Mr Murdoch said he had not been approached for comment before the June 29 article and subsequent related pieces published on the Crikey website, and had only complained to Private Media four times in five years.

He is also seeking injunctions barring the publication and promotion of the allegedly defamatory articles.

Mr Hayward said Crikey has intended to bring the use of defamation law by the rich and powerful into the light.

"Taking on this fight is risky, and we are not foolish enough to predict its outcome," he said.

"However, we believe that there is an issue of fundamental public importance at stake, and that is why we are defending the case brought against our company and our journalists."

Australian Associated Press