The Turnbull government faces a tumultuous end to the parliamentary year as Labor threatens to take advantage of the coalition's depleted numbers amid the citizenship scandal.
As the foreign citizenship saga claimed another Liberal MP in John Alexander on Saturday, Labor warned it would use the final sitting weeks to pursue its own agenda.
Mr Alexander announced his resignation from parliament on Saturday, saying he "most likely" holds UK citizenship.
The member for Bennelong said he'll stand again for parliament in an upcoming by-election in a seat the Liberals hold by more than nine per cent.
The former tennis star's departure temporarily leave's the coalition clinging to 73 seats in the 150 seat House of Representatives, not counting the Speaker.
While Labor, which has 69 seats, has ruled out challenging the government with a no confidence motion, it has the big banks in its sights.
Labor MP Tony Burke says his party will try to deliver on a royal commission into banks, despite the numbers still being stacked against them.
"When we get back to the Parliament what Labor will do with the new situation is pursue our agenda," Mr Burke told reporters on Saturday.
"Our commitment whatever the numbers on the floor are, is to be representing the people who have been hurt through the banks without getting a royal commission."
Despite yet another of his team falling foul of section 44, Prime Minister Malcolm Turnbull ruled out returning early from his trip to Asia.
"These are very important meetings, huge priorities," Mr Turnbull told reporters in Da Nang, Vietnam where APEC summit was wrapping up, before heading to Hong Kong.
Mr Turnbull said he spoke to Mr Alexander on Friday night ahead of his resignation.
"John's done the right thing. The honourable thing," Mr Turnbull said.
Earlier this week, Mr Alexander sought advice on whether he is a UK citizen through his father Gilbert Alexander, who was born in England in 1907 and arrived in Australia in 1911.
Mr Alexander said he hadn't received official confirmation of his dual citizenship, but said the "balance, the probability of evidence is that I most likely am".
"The obligation that I have is that once I do not hold the view that I'm solely Australian I must resign," Mr Alexander told reporters in Sydney.
He will be the second member of the House of Representatives forced to resign because of their dual citizenship.
Barnaby Joyce is facing a by-election in New England, after discovering he was a New Zealand citizen, because of his father's birth.