One Nation senator Malcolm Roberts could replace himself if it's found he was ineligible to run for parliament.
The Queensland senator is facing questions over whether he held British citizenship at the time he ran for election in mid-2016.
Senator Roberts insists he sought to renounce any possible British citizenship before nominating but he did not receive a written reply from British authorities until six months later, well after he was elected to the Senate.
If he is referred to the High Court and disqualified under section 44 of the constitution - which bans dual nationals from being MPs - the next candidate on the Queensland One Nation ticket would take the seat.
That candidate, Fraser Anning, is facing bankruptcy proceedings in the Federal Court, which if proven would render him ineligible to be in parliament.
However, if the bankruptcy status only applies to Mr Anning after the election period it will trigger a casual vacancy - not a recount - meaning any One Nation member could take the seat.
If he was an ex-senator at that point, Senator Roberts could then take back his old seat, having only been officially confirmed as solely an Australian citizen last December.
Senator Malcolm Roberts Source: AAP
It is understood the government has made no decision to ask parliament's upper house to refer Senator Roberts to the High Court.
However, it will ask for stood-aside minister Matt Canavan to be referred to the court to test whether his Italian citizenship rendered him ineligible to continue in the Senate.
The Greens will ask the Senate to refer the cases of Larissa Waters and Scott Ludlam to the High Court, after the two deputy leaders resigned over their dual citizenship with Canada and New Zealand respectively.
The party will also seek separate Senate and House inquiries into the eligibility of all members and senators, as well as whether any MPs have defrauded the commonwealth by running for parliament knowing they were ineligible to do so.
The two inquiries would be advised by independent auditors who would check the documentation of MPs.
If MPs do not comply with requests for information they could be suspended from voting in parliament until they do so.
Any MPs identified by the inquiries as potentially having breached the constitution could be referred to the High Court to test their eligibility.
