A former election candidate has created a legal dilemma after challenging Nick Xenophon's endorsed replacement for his place in the Senate.
Mr Xenophon has resigned from the Senate to contest the March 2018 South Australian state election, endorsing his principal adviser Rex Patrick to replace him.
But the South Australian parliament - which needs to hold a joint sitting to endorse a replacement - has received a nomination from Nick Xenophon Team 2016 candidate Tim Storer and advice is being sought on how to deal with the unusual situation.
SA Premier Jay Weatherill told state parliament on Wednesday he had received a letter from lawyers representing Mr Storer.
"Mr Storer asserts rights in relation to the filling of the casual vacancy," Mr Weatherill said.
The premier has asked his attorney-general to seek legal advice from crown solicitors.
That advice would inform deliberations of the joint sitting to be held on November 14 to replace the senator.
Mr Xenophon has lodged an application with the Australian Electoral Commission to change his party name from NXT to SA Best (Federal), however, the registration is being held up by the New England by-election.
He and Mr Storer ran on the NXT ticket at the 2016 election.
The High Court last week cleared Mr Xenophon of having any problem under section 44 of the constitution, which bans dual citizens from parliament.
However, he resigned from the Senate anyway in a bid to hold the balance of power in the SA parliament.
If the court had found Mr Xenophon ineligible, Mr Storer was due to replace him having been the next candidate on the NXT ticket.
Constitutional expert Professor George Williams told AAP section 15 of the constitution suggested the person selected should be of the same political party as the person who created the vacancy.
"As Xenophon has not been disqualified, there is no requirement for a count back," he said.
"This means that the selection is made via a casual vacancy under section 15 of the constitution, which gives the party discretion as to who it chooses from its own membership to fill the vacancy. No person has any right to that vacancy."
