Australian independent senator Jacqui Lambie has become the eighth lawmaker to resign over dual citizenship.
In a tearful speech, she told the Senate she had recently learned she held British nationality through her father and grandfather.
The constitution says MPs must be citizens of Australia only. Politicians found to have dual citizenship have included the Deputy PM Barnaby Joyce.
The issue has put the centre-right government in a precarious position.
Prime Minister Malcolm Turnbull’s Liberal Party has already lost its majority in parliament, and a recent opinion poll showed his popularity at a new low.
Jacqui Lambie, the 46-year-old senator for Tasmania, said that following the recent revelations, she had made her own enquiries and “it is with great regret that I have to inform you that I have been found ineligible by way of dual citizenship”.
She told the Senate she had understood from her father that the family had renounced its British citizenship years ago. But she said she did not blame him for what had since come to light.
“It’s not because of him I’m leaving this place, it’s because of him I was here in the first place,” she said tearfully.
Under Australia’s 116-year-old constitution, dual citizens are banned from running for federal office. A court clarified recently that being unaware of another citizenship is not grounds for exemption.
Critics argue that the constitution should be changed in a country where more than half of the population of 24 million was either born overseas or has parents born overseas.
Two lawmakers who were forced to resign over the issue will stand again for their seats in by-elections in December, having renounced their dual citizenship.
But the Liberal Party’s John Alexander faces a tough fight in his Sydney district after the opposition Labor Party put forward Kristina Keneally, a popular former state premier of New South Wales, to contest it.
Australia dual citizenship: Jacqui Lambie latest lawmaker to go}