Opposition Leader Bill Shorten has known for more than a week that his close factional ally David Feeney was struggling to prove he renounced his British dual citizenship, as Labor continues to resist government demands to refer more of its MPs to the High Court.
The Senate on Wednesday referred Labor senator Katy Gallagher's eligibility to the court, despite the ALP's continued insistence she's in the clear.
She is the first Labor figure to be referred but the government believes four lower house Labor MPs should join her: Mr Feeney, Justine Keay, Susan Lamb and Josh Wilson.
Labor believes at least four Coalition MPs have further questions to answer: frontbencher Josh Frydenberg and backbenchers Jason Falinski, Nola Marino and Julia Banks. All claim to be in the clear but have so far produced incomplete documentary evidence.
It's understood Labor would agree to the referral of its own members - as well as crossbencher Rebekha Sharkie - if the government were to agree to refer some of its own. But the government is digging in, insisting none of its people have reasonable doubts.
Ms Keay, Ms Lamb and Mr Wilson tried to renounce their citizenship prior to the 2016 election, but failed to receive confirmation until after the close of nominations.
Labor accepts all its people are likely to be referred, with Barnaby Joyce expected back in the chamber later today to give the government its majority back.
Mr Feeney's case is the most obviously problematic.
He approached Mr Shorten early last week to tell him he could not locate any renunciation documents and he was seeking further advice, Fairfax Media has learned.
Mr Shorten told Mr Feeney - a key Victorian ally and close personal friend who was best man at the Labor leader's wedding - that he had until the December 5 deadline to produce the proof or he would face possible High Court referral, sources say.
Mr Feeney appears to have known for at least two weeks he was in potential trouble, because that is when he deleted an old tweet referring to the citizenship crisis saying: "Noticed how the Turnbull Govt has strangely stopped mocking the Greens Party for incompetence and sloppiness?"
On November 30, Mr Shorten was maintaining that he believed the ALP had done its job and its governance standards were "demonstrably superior" to other parties.
Mr Feeney has agreed to refer himself to the court if he cannot produce his documents by the end of the week. If he is disqualified, his seat Melbourne seat of Batman would go to a byelection that even Labor Party hardheads believe they would be likely to lose to the Greens.
With Barnaby Joyce set to return to the lower house later on Thursday, the government will be able to use its majority to refer the Labor MPs to the court against their will.
Senator Gallagher resigned her frontbench and parliamentary roles after the Senate's referral.
"While I do not agree with the need for this referral, I do not resent it," she said.
"The success and standing of the Australian Senate is bigger than all of us, and should be focused solely on what we are able to deliver together for the Australian people.
"It is bigger and much more important than the circumstances of individual senators, and acting in a way which protects the reputation, the legitimacy, the confidence of our parliamentary institutions, should always, in my humble opinion, be paramount."
Documents provided to the Senate this week showed she was "at the date of her nomination for the 2016 election, a British citizen by descent" and that her moves to renounce in April 2016 took until August 16 to be completed by British officials.
Labor's pursuit of Energy Minister Josh Frydenberg has also begun to split the party, given his parents arrived in Australia stateless after escaping the Nazis. Two Labor MPs - Ed Husic and Michael Danby - have broken ranks to criticise the decision to target Mr Frydenberg.
Labor's legal affairs spokesman Mark Dreyfus attacked Mr Frydenberg for not lodging any paperwork to prove he is not a dual citizen.
Mr Danby told the Australian Jewish News: "My view is the Dreyfus approach is just political tactics and not cognisant of the wider political, historical and ethical issues."
And Mr Husic said: "If we get to the point where we're pursuing people who were stateless and escaping one of the most horrific episodes in modern history, well I'd be interested to see how far we do pursue this."
???The High Court meanwhile appears to have shut the door on a return to the Senate by former deputy Nationals leader Fiona Nash. The court found that the original Liberal replacement for Ms Nash - Hollie Hughes - was not eligible for election, rather than becoming ineligible afterwards.
Constitutional expert Anne Twomey said that paved the way for conservative hardliner and Tony Abbott ally Jim Molan to take up the seat.
"The court held that the original election was not completed, so Hughes was disqualified during the ongoing election period. Hence, it is resolved by a recount, not by a casual vacancy," Professor Twomey said.???