The High Court has ordered recounts of the 2016 election result to find replacements for resigned senators Jacqui Lambie and Stephen Parry.
The two senators – both from Tasmania – quit the parliament last month after they discovered they were both UK-Australian dual citizens.
The Jacqui Lambie Network leader and Liberal Senator Stephen Parry, who was also the former Senate president, were among nine federal politicians to leave the parliament this year over dual-citizenship concerns.
Unlike the Lower House members John Alexander and Barnaby Joyce who need to win by-elections to return to the parliament, senators are generally replaced by whoever was next on their party’s ticket at the last election.
Fraser Anning, Jordan Steele-John and Andrew Bartlett have all entered the Senate in the past few weeks to replace disqualified One Nation and Greens senators.
Ex-senator Lambie's position would normally go to the next person on her Jacqui Lambie Network ticket in the 2016 election, following the recount.
But the next person on the party's list may not be able to replace her.
A constitutional expert told AAP on Monday there are doubts around Senator Lambie's possible replacement, Devonport Mayor Steve Martin.
Professor George Williams, from the University of NSW, said Mr Martin could be in difficulty because of his local government position.
Whether a local council position is an "office of profit under the Crown" - a ground for disqualification under the constitution - has been a grey area in constitutional law.
"The High Court would need to decide," Prof Williams told AAP.
Ex-senator Parry’s position would likely go to the next Liberal on the Tasmanian senate ticket, Richard Colbeck.
Mr Colbeck has served as a senator before.
But his appointment is not a sure thing, because the Tasmanian recount may be harder to predict than in other states.
Many Liberal voters in the Tasmanian senate election voted below the line, meaning they allocated their preferences manually according to their personal choices.
That could mean another candidate is elected to fill Stephen Parry’s place.
Nick Xenophon Team senator Skye Kakoschke-Moore also quit after discovering a latent British citizenship.
The High Court has agreed to deal with her case in January. Her lawyer will attempt to argue that Ms Kokoschke-Moore should be allowed to be included in the recount as she has now renounced her British citizenship.
