Five more Australian MPs leave parliament after court's citizenship ruling

Government Orders Dual Citizenship MPs To Resign By The End Of The Day

The High Court rules Labor Senator ineligible over dual citizenship

In what was widely viewed as a fresh test case, a high court ruled Senator Katy Gallagher ineligible, the BBC reported.

Labor leader Bill Shorten said three of the ousted MPs would seek re-election.

Adherence to the dual-citizenship rule, in a country where more than half the population of 24 million were either themselves, or have a parent, born overseas, came under the spotlight past year, with the High Court adopting a strict interpretation of the law.

Ms Gallagher said she was "deeply disappointed" with the outcome, making her the 11th politician to be booted out of Parliament.

The High Court has disqualified ACT Labor senator Katy Gallagher from sitting in parliament, in a decision opening the way for four byelections, three of them in Labor seats.

The citizenship crisis has claimed nine federal parliamentarians since the election.

The decision will increase the pressure to resign on three Labor MPs Josh Wilson (Fremantle, Western Australia), Justine Keay (Braddon, Tasmania) and Susan Lamb (Longman, Queensland), as well as the Centre Alliance's Rebekha Sharkie (Mayo, South Australia) because they have relied on the same defence.

Chief Justice Susan Kiefel said the British renunciation process was "simple" and concluded Senator Gallagher did not take sufficient steps to rid herself of dual citizenship before her nomination.

"I believe that I have more to contribute to public life and I will take the time to talk with Labor Party members on how I can do this over the months ahead", she said.

The fate of the Labor MPs' coupled with the resignation of Perth's Labor MP Tim Hammond will see five by-elections take place, a very costly exercise.

Sharkie said she would now take urgent legal advice.

At a hearing in March, lawyers for the government argued Ms Gallagher failed to renounce her United Kingdom citizenship before the last election because she left the application too late and did not attach the right documents to her letter to authorities. My paperwork was lodged and received by the UK Home Office before the election was called.

"Former Senator Gallagher is an outstanding Senator and she is an important part of Labor's Senate leadership team", Ms Wong said.

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