One Nation's Malcolm Roberts looks to be headed to the High Court over questions about his citizenship.
The senator's colleagues are expected today to pass a motion referring him to the court over suggestions he did not renounce his British citizenship in time to nominate for parliament.
The motion will be moved by the Greens, and is likely to receive widespread support, even from One Nation's closest allies on the crossbench.
"On the facts alone I would support that, but I will listen to the debate," Liberal Democrat senator David Leyonhjelm told AM.
The ABC has confirmed senators Jacqui Lambie, Derryn Hinch and Cory Bernardi also support the motion, the latter another One Nation ally.
It is understood Senator Roberts met with key crossbencher Nick Xenophon in a bid to secure a vote against the motion, but that the Nick Xenophon Team will ignore that plea and vote with the Greens.
Labor senator Doug Cameron confirmed to AM the Opposition would also support the motion, giving it more than enough votes to succeed.
Senator Cameron is himself a former holder of British citizenship, which he renounced prior to nominating for parliament.
"I had to get what's called a form RN1, had to fill the form in in duplicate," he told AM, adding the process took months.
"I received what's called a stamped copy of the declaration of renunciation and that constitutes formal evidence I ceased to be a British citizen.
"So Senator Roberts should have all that."
Brandis says Roberts deserves benefit of the doubt
The Government now appears to be Senator Roberts' only supporter in the Senate, outside his own party.
Leader of the Government in the Senate, George Brandis, told Sky News that Senator Roberts' declaration that he was entitled to sit in Parliament should be believed.
"When a person lodges an apparently regular nomination for an election, and they are declared to have been elected, then the onus of proof, as it were, lies on those who seek to prove that they weren't validly elected that that is the case," he said.
"It is a very serious matter for a group of politicians sitting in a parliamentary chamber to put a question mark over the eligibility of one of their number."
One Nation and Senator Roberts both declined the ABC's request for a comment.
