A constitutional crisis blighting Australian politics resurfaced Wednesday with a string of forced resignations among opposition Labor party MPs, handing the government hope of boosting its slim parliamentary majority.
The High Court in Canberra ruled upper house senator Katy Gallagher ineligible to hold her seat as she had not renounced her British citizenship prior to the last election in 2016.
The decision triggered the resignation of three more opposition parliamentarians and a member of the minority Centre Alliance party, who all believed the court ruling would also apply to their circumstances.
The four MPs all sit in the lower house of parliament, forcing by-elections in their constituencies.
"In good faith, our candidates and the Labor party and I have relied on advice that's been the same advice for over 20 years," embattled opposition leader Bill Shorten told reporters in Canberra.
"But the High Court has looked at the facts in Senator Gallagher's matter, they have developed a new test, a stricter test, and we have accepted that."
Adding to Labor's woes, another MP quit due to family commitments, which in total forces five by-elections.
The marginal Queensland seat of Longman appears most at risk with Labor MP Susan Lamb securing it at the last election with less than a one percent margin.
The citizenship crisis came to a head in October when the High Court reaffirmed an obscure provision in the country's 1901 constitution that forbids dual citizens from serving in federal parliament, forcing a slew of resignations.
Most were from the Senate, the upper house, but two were from the lower House of Representatives, where the ruling Liberal-National coalition holds only a one-seat majority.
Then deputy prime minister Barnaby Joyce was among those forced to step down after he discovered he had automatically acquired New Zealand citizenship through his father.
Joyce and a fellow coalition MP were successfully re-elected after contesting by-elections, preserving the government's wafer-thin majority.
The conservative ruling-party has accused Labor of harbouring potential dual citizens since the saga began, calling for the resignation of those they believed could not prove their status.