The conservative Liberal spent 40 minutes at a Senate estimates hearing drilling senior officials about social media posts from a communications director at the aged care royal commission.

Senator Stoker tied the tweets to a recent High Court case where a public servant's online posts were found to breach the code of conduct because they were critical of the federal government.

The media staffer's personal Twitter profile does not mention she works for the royal commission.

Senator Stoker took officials through a printed list of tweets and re-tweets, including one telling Scott Morrison to rack off to Hawaii, referring to the prime minister taking an overseas holiday at the height of the bushfire crisis.

"She's re-tweeted a picture of a bus, where the prime minister is described as a Liberal muppet," Senator Stoker said.

"The next page, we have a cartoon that is titled Mr Prime Minister-Head, a reference to Mr Potato Head, the much-loved children's toy.

"It's hard to know which bit is the piece de resistance, in this theatre of clear anti-Liberal sentiment."

James Popple, the official secretary to the royal commission, said the media director was doing a great job.

"But the information you've just given me and given us, is new to me and I thank you for bringing it to our attention," Dr Popple said.

Secretary of the Attorney-General's Department Chris Moraitis said he was not previously aware of the staffer's tweets but would look into the issue.

"But I don't want to say anything here that might affect any future decision makers' approach to both the facts of the case and decision on breach of the code."

The aged care royal commission is nearing completion after hearing the system is littered with failures, rife with abuse and in urgent need of more government funding.

Senator Stoker is concerned the staffer's personal Twitter account could affect the inquiry's integrity.

Labor senator Anthony Chisholm tried to ask Dr Popple about the more than 680 deaths in aged care from coronavirus.

"That's not relevant to matters being examined by this committee," Senator Stoker said.

"This is about the proper processes for running a royal commission, if you want to talk about deaths from COVID, there's the COVID committee to deal with that."

Prime Minister Scott Morrison defended Senator Stoker's line of questioning and argument that aged care deaths were not relevant to the hearing.

"It's important that the commission engage in its work in a way that is completely nonpartisan and completely independent," he told parliament.

"I see it as the job of Senate estimates to probe into matters regarding integrity."

Senator Stoker has long campaigned for freedom of speech in universities.

She has previously admitted to using a pseudonym on social media to defend against her attackers, agree with her supporters and promote her political views on controversial topics including race and gender.

Australian Associated Press