Deputy Nationals leader Fiona Nash has told parliament she believes she may be a dual British citizen by descent, and will refer herself to the High Court to consider whether she is eligible to sit in the Senate.
Nash revealed her citizenship issues on Thursday evening before the Senate rose for a two-week break. When parliament resumes she will move a motion to refer herself to the High Court.
Nash said she approached the British Home Office on Monday, after the deputy prime minister Barnaby Joyce announced he was a dual New Zealand citizen.
"By Monday evening I was advised that a case worker at the UK Home Office was of the view that on the basis of the limited facts I had provided I was a British citizen by descent by my Scottish-born father," Nash said.
Nash entered parliament as a Nationals senator for New South Wales in 2005.
She said growing up her parents had told her she wasn't a dual citizen and that in order to receive UK citizenship she would have to apply for it.
Her parents divorced when she was young, and she had little contact with her Scottish-born father during his life. He died nine years ago.
Prime minister Malcolm Turnbull has told Nash she doesn't have to resign as a minister or deputy Nationals leader, or quit the Senate.
One Nationals senator told BuzzFeed News that "this is crazy" and he had no idea what was going on.
Nash is the sixth politician that has been referred to the High Court under Section 44.1 of the constitution that says dual citizens are not allowed to serve in the Australian parliament.
Greens senator Scott Ludlam resigned last month after discovering he was a dual citizen with New Zealand.
Shortly after Ludlam's resignation, former Greens senator Larissa Waters discovered she was a dual citizen of Canada.
The following week, senator Matt Canavan stepped down from his role as resources minister after discovering that his mother had signed him up as a dual citizen with Italy.
Last week, One Nation senator Malcolm Roberts was referred to the High Court by his own party after it was revealed he had once signed he was a British citizen.
Earlier this week deputy prime minister and Nationals leader Barnaby Joyce revealed he was a New Zealand citizen.
Here's the video of Fiona Nash telling the Senate (minutes before it rose) that she might be a UK citizen.