Malcolm Turnbull has taken a swipe at three Labor MPs caught up in the dual-citizenship saga for delaying their resignations from federal parliament.
Susan Lamb, Josh Wilson and Justine Keay signalled on Wednesday they would quit their lower house seats following the High Court's decision to disqualify Labor senator Katy Gallagher.
"They have said they are ineligible, they have acknowledged they are ineligible and they still have not resigned, so they are drawing salaries and using MPs entitlements," the prime minister told ABC radio on Thursday.
Labor finance spokesman Jim Chalmers said his colleagues would formally resign on Thursday after settling some electoral matters.
The opposition is on the back foot over the issue after insisting none of its MPs would be caught out by the dual-citizenship requirements of the constitution.
Ms Gallagher was deemed a citizen of a foreign power - the United Kingdom - when the writs for the 2016 federal election were issued.
Her three Labor colleagues and independent Rebekha Sharkie - who quit her South Australian seat on Wednesday - were in the same situation.
Opposition frontbencher Tony Burke argued Labor had tried to refer the MPs as part of package deal with coalition MPs under a citizenship cloud.
"It's ended up where it has. We're now in by-elections and the resignations will be in today for those members and they're off in their electorates fighting their campaigns," he told Sky News.
Labor has turned the spotlight on Liberal backbencher Jason Falinski, who insists he doesn't hold Polish citizenship.
The MP lodged a new letter from the Polish Embassy on Wednesday.
"I can confirm that according to our records you have never had a Polish passport or a Polish identity card, and you have never applied through our Embassy to relevant Polish authorities to confirm the possession of Polish citizenship," the ambassador wrote to Mr Falinski.
But Mr Burke says he can't reconcile that with documents held by the National Archives showing Mr Falinski's father and paternal grandparents all declared their nationality as Polish in 1958.
With the early retirement of Labor MP Tim Hammond, five lower house by-elections now need to be conducted.
They are likely to be held on the same day, with June 16 the earliest possible date for a Super Saturday poll.
Mr Turnbull said the polls would "obviously be a very big test" for Labor leader Bill Shorten who asserted his party's vetting processes were "rolled gold".
"A rolled-gold guarantee from Bill Shorten isn't worth a cracker," the prime minister told reporters in Queanbeyan.
The Greens claim the independent panel the minor party recommended could have determined the eligibility of all MPs.
"Here we are in the middle of a budget, we've got politicians talking about themselves again because neither side has acted with integrity on this," leader Richard Di Natale told ABC radio.