Federal Resources Minister Matt Canavan has resigned from the frontbench to check the status of his dual Italian-Australian citizenship.
But the government has raised doubts about whether he is in breach of rules forbidding parliamentarians from holding dual nationality.
Senator Canavan announced he was standing down on Tuesday to clarify his citizenship status because his mother is Italian.
"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 told reporters.
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."
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."
