Prime Minister Malcolm Turnbull came "perilously close" to directing the High Court to rule his deputy Barnaby Joyce was validly elected to Parliament, the shadow attorney-general says.

Key points: Shadow Attorney-General said Malcolm Turnbull came "perilously close" to directing the High Court over Barnaby Joyce's citizenship

Shadow Attorney-General said Malcolm Turnbull came "perilously close" to directing the High Court over Barnaby Joyce's citizenship Mr Turnbull said Mr Joyce was "qualified to sit in the house and the High Court will so hold"

Mr Turnbull said Mr Joyce was "qualified to sit in the house and the High Court will so hold" The Attorney General said Mr Turnbull was simply commenting on the party's legal advice

The Deputy Prime Minister has been referred to the court after the New Zealand Government confirmed he is a dual citizen, potentially ruling him ineligible to sit in Parliament.

Shadow attorney-general Mark Dreyfus criticised Mr Turnbull for saying Mr Joyce was "qualified to sit in the house and the High Court will so hold".

"These were the comments of an arrogant prime minister who came perilously close to directing the High Court," he told the ABC.

"I don't think he understands that the separation of powers requires just that — a separation.

"I think the High Court justices will probably put it to one side, but they would be struck by how unusual that tone and that kind of comment is from a serving prime minister."

But Attorney-General George Brandis said the comment was "not a directive at all" and the Prime Minister was simply commenting on the party's legal advice.

"The Prime Minister is a very accomplished lawyer and has practiced before the High Court and knows that better than anyone," he told Lateline.

"What the Prime Minister was saying was expressing a view about the law which he expects the High Court will uphold, and that view was based on the Solicitor-General's advice."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 9 minutes 14 seconds 9 m George Brandis says Malcolm Turnbull was acting on legal advice

Senator Brandis said the legal issue surrounding Mr Joyce was not whether he was a dual citizen, but whether he took reasonable steps to comply with Section 44 of the constitution.

"The legal issue here is not whether he is a citizen of New Zealand, but whether in the circumstances of this case, when he had no idea at all that he was a dual citizen," he said.

Labor won't release proof of MPs' eligibility

Sorry, this video has expired Barnaby Joyce says he'll ask the High Court to rule on his citizenship

Coalition frontbencher Christopher Pyne has warned Labor MPs against opening "Pandora's box" on citizenship, claiming many Labor MPs may have been dual citizens when elected.

In Parliament, Mr Pyne named Labor MPs Susan Lamb, Tony Zappia, Justine Keay and Maria Vamvakinou, saying they had yet to publicly prove they were validly elected.

"The reality is there are more and they need to prove that they are not disqualified from sitting in the House of Representatives," he said.

The four MPs named by Mr Pyne did not share their paperwork with the ABC on Monday night, but pointed to a statement by the party's national secretary Noah Carroll.

"We are confident every member of the Labor caucus has been properly elected," Mr Carroll said.

The ABC contacted Opposition Leader Bill Shorten's office requesting documents to prove the citizenship status of the four MPS, but was told "we are satisfied with the party's processes".

Mr Dreyfus said there was no need for the MPs to make their documents public.

"Christopher Pyne said not one single thing that cast doubt on their eligibility to serve," he said.

Mr Joyce's case has prompted Greens leader Richard Di Natale to renew his calls for an audit of all federal politicians' citizenship.

"There is one way to determine this once and for all, rather than having this dribble out with another person and then another person, with people ultimately throwing their hands up in despair at what's going on," Senator Di Natale said.

"That's a comprehensive audit."