The political future of rising coalition star Matt Canavan is set to rest in the hands of the High Court after the former federal resources minister revealed the Italian government has him registered as one of its citizens.
The government has raised doubts about whether Senator Canavan is in breach of rules forbidding parliamentarians from holding dual nationality.
Senator Canavan announced he was standing down from the cabinet on Tuesday to clarify his citizenship status.
"I have become aware that according to the Italian government, I am a citizen of Italy," Senator Canavan told reporters.
In 2006, his mother applied for citizenship and in doing so she made an application for the then 25-year-old as well.
"I had no knowledge that I, myself, had become an Italian citizen - nor had I requested to become an Italian citizen," Senator Canavan said.
His mother raised with him the possibility that he may be a citizen after the resignations of Greens deputy leaders Larissa Waters and Scott Ludlam.
Senator Canavan then checked his citizenship with Italian authorities, which confirmed the application was not signed by him.
"I have not been able to obtain definitive legal advice as to whether my registration as an Italian citizen, without my knowledge or consent, was valid under Italian law. I am seeking to obtain that advice presently."
The Deputy Prime Minister and Leader of the Nationals, Barnaby Joyce, said he was standing behind Senator Canavan's explanation.
"One would presume that if something happens without your knowledge, and without your consent, then it's probably an invalid process," he told reporters in Canberra on Wednesday.
"This was something that, two days ago, took us all by surprise when we found out that he was registered as an Italian citizen."
When questioned about the validity of Senator Canavan's explanation, given the rigorous process to become an Italian citizen, Mr Joyce said it was up to the High Court to deliberate on it.
"Senator Canavan has stated to me that he did not complete any forms, so it was a discussion the family had and he thought that's where it's rested. I think they've found the forms and they're unsigned."
Attorney-General George Brandis says Senator Canavan may not be in breach of rules forbidding dual citizens from holding office because the Queensland senator was unaware of the application made on his behalf by his mother.
"It is the government’s preliminary view that because the registration was obtained without Senator Canavan’s knowledge or consent that he is not in breach of Section 44 of the Constitution."
Section 44 states: "Any person who is under any acknowledgement of allegiance, obedience, or adherence to a foreign power, or is a subject or a citizen or entitled to the rights or privileges of a subject or citizen of a foreign power... shall be incapable of being chosen or of sitting as a senator or a member of the House of Representatives."
Senator Brandis said the government had taken advice from the Solicitor-General and experts in Italian law on the issue.
"Nevertheless, in view of the legal uncertainty concerning the matter, when the Senate convenes on Tuesday week, the government will move to refer the matter for determination by the High Court."
But Labor frontbencher Tony Burke raised doubts about the explanation given.
"I've tried to piece together how it is that something like this or why on earth something like this would be kept secret from him," he told ABC's Lateline program.
"You've got to presume that will be tested before the courts."
Mr Burke also pointed to recent criticism by Prime Minister Malcolm Turnbull of the Greens' dual citizenship blunders in which he blasted the minor party's "sloppiness".
"I think Malcolm Turnbull would be regretting those words now."
Italian citizenship is determined by blood right - a child whose parent, or parents, are Italian is automatically considered a citizen.
Senator Canavan was elected to the upper house in 2013 and has been the Resources Minister for just over a year.
Mr Joyce will be taking over the Resources and Northern Australia portfolio until Senator Canavan's status is resolved.
Meanwhile, One Nation Senator Malcolm Roberts has called for an inquiry into the eligibility of all sitting MPs and Senators for office.
The Indian-born Senator on Tuesday produced documents including a statutory declaration claiming he is eligible to stand for parliament.
"To maintain the integrity of parliament, I propose an appropriate office conduct a review into the eligibility of all parliamentarians to continue sitting in the Australian parliament," he said on Facebook.
"Until the inquiry, my stat dec (sic) stands. My renunciation documentation will be provided to this inquiry."
-With AAP
