Bill Shorten is withholding support for Malcolm Turnbull's plan to resolve the citizenship crisis, insisting MPs should be given five days rather than three weeks to produce their documents and dismissing the need for Parliament to be recalled days before Christmas.
As Mr Turnbull waits to hear whether Liberal MP John Alexander will be forced to resign - sparking a byelection in his Sydney seat and threatening the government's majority - he has sought to turn the tables on Labor by thrusting one of its MPs into the citizenship spotlight.
The Prime Minister says that under the High Court's strict black-letter ruling last month, Labor MP Justine Keay, who sought to renounce her British citizenship in May last year but didn't have it confirmed until after the July election, is now under a cloud.
"She has acknowledged she was a UK citizen at the time she nominated. That creates an issue," Mr Turnbull said. "She's ticked a box which says she's in compliance with section 44 and one of the requirements is you not be a citizen of another country.
"If she wishes to maintain her position in the Parliament and not resign, that's going to involve some considerable legal debate."
But Mr Shorten has dismissed the concerns about Ms Keay and fellow Labor MP Susan Lamb, saying he is confident they would satisfy the court's "reasonable steps" test.
"I'm not about to take legal advice from Mr Turnbull, am I? He got it so wrong with his own ministers, his own deputy prime minister and now the president of the Senate. I am confident Labor has pretty exhaustive vetting procedures and I'm confident steps have been taken," he said.
Mr Turnbull met with Mr Shorten for two hours of talks in Melbourne on Wednesday as he seeks support for his new parliamentary disclosure rules, which would require all MPs to publicly reveal their family history, citizenship status and supporting documents.
But the leaders failed to reach an agreement, with Mr Shorten maintaining the proposed rules are not strict enough and should require more information.
"We want to sharpen up the Prime Minister's resolution and make sure it is foolproof," Mr Shorten said.
He also believes MPs should be given just five days to produce their information once the new rules are passed, not the 21 proposed by Mr Turnbull. That would allow Parliament to refer any suspect MPs to the High Court before it is due to rise for the year in early December.
Under Mr Turnbull's original proposal, Parliament may need to be recalled just before Christmas - at a cost of up to $1 million a day - to refer any MPs exposed by the new disclosure rules. The High Court is expected to rise for its summer break on December 15.
Mr Turnbull said it was a "constructive discussion" and indicated he was open to negotiation with Mr Shorten about detail and timing.
Their meeting came as Mr Alexander anxiously awaits advice from the UK Home Office about his citizenship status. He is expected to receive advice on Thursday.
The former tennis professional is suspected to have attained citizenship by descent from his British-born father. He has never renounced but "understands" his father did.
If he is found to be a dual citizen Mr Alexander is expected to resign, sparking a byelection in his Sydney seat of Bennelong. The 67-year-old has confirmed he intends to run again.
Five MPs, including former deputy prime minister Barnaby Joyce, were disqualified from Parliament because of their dual citizenship last month. A sixth, former Senate president Stephen Parry, resigned a few days after the verdict, confirming he too was a dual citizen.
Four Liberal MPs have thrown their hat in the ring ??????to replace Mr Parry as president, including Special Minister of State Scott Ryan and backbenchers Ian Macdonald, David Fawcett and Dean Smith.
with Noel Towell