The fate of the deputy prime minister, Barnaby Joyce, will be determined on Friday by the high court in a decision that could end the terms of three senior Turnbull government figures, or lift doubt on their status and provide a major boost for its political fortunes.
The court will deliver judgment at 2.15pm on seven politicians’ eligibility to sit in parliament, which was challenged because they held dual citizenship at the 2016 election.
Win or lose, the court decision will cap off a rugged week for the government.
The employment minister, Michaelia Cash, on Thursday survived a political assault from Labor, with Malcolm Turnbull forced to defend her after it was revealed a staff member tipped off the media before controversial AFP raids on Australian Workers Union headquarters in Sydney and Melbourne on Tuesday.
With Labor on the offensive both in the House and in Senate estimates hearings, Turnbull declared Cash had “acted entirely properly” and could not be held responsible for the activities of a staff member who has misled her.
In a matter of public importance after question time Bill Shorten upped the stakes, telling the house “Australia has a grubby government and an increasingly grubby prime minister”.
“And during question time this point was most clearly illustrated when the prime minister had a chance to defend Senator Cash when the opposition moved a resolution condemning her – they did not defend her, they simply gagged the debate,” he said.
Shorten invoked Turnbull’s own standard during the Utegate affair that ended his stint as opposition leader to argue that misleading parliament “should result in the dismissal or resignation of a minister”.
He said Cash had misled the Senate five times, which Cash has denied, citing the fact her senior media adviser “misled” her and acted without her knowledge and authorisation when leaking details of the AFP raids.
Although Cash will not appear at an extra Senate estimates hearing on Friday, Labor and the Nick Xenophon Team have flagged an independent inquiry into the media tip off about the AWU raid, which could be launched when the Senate returns on 13 November.
The controversy over Cash came as nervousness within the Coalition increased ahead of the high court ruling.
The “citizenship seven” are: Joyce, deputy Nationals leader Fiona Nash, former resources and Northern Australia minister Matt Canavan, One Nation senator Malcolm Roberts, senator Nick Xenophon and former Greens senators Larissa Waters and Scott Ludlam.
Joyce will face a byelection in New England if found ineligible, while senators will be replaced by a recount likely to return the next candidate on their parties’ 2016 Senate ticket.
If Joyce is found ineligible, the Turnbull government will have 75 lower house seats, making it more likely to lose house votes unless the Coalition retains Joyce’s seat against a likely run by former independent MP Tony Windsor.
The court will deliver reasons for judgment interpreting section 44 of the constitution which bans subjects or citizens of a foreign power from sitting in parliament.
The commonwealth argued that MPs or senators need to have “voluntarily obtained or retained” their foreign citizenship, requiring knowledge of their dual citizenship in order to be disqualified.
The former solicitor general Justin Gleeson argued on behalf of Windsor that would lead to “radical instability” and, except in exceptional circumstances, status as a foreign citizen should be enough to disqualify them.
Xenophon has said he will contest the South Australian election regardless of the result. For Xenophon, Waters and Ludlam the case will decide whether their replacements are chosen by their party or through a recount, although of those three, only Waters is seeking to remain in the Senate.
Guardian Australia understands that Liberal Hollie Hughes, who held the sixth spot on the New South Wales Senate ticket would seek to retain Nash’s seat if the recount shows she has won it.
Canavan has suggested he would consider quitting politics if found ineligible. If he is found ineligible, Canavan’s Queensland Senate seat would likely be won former Queensland Liberal senator, Joanna Lindgren, in a recount election.
