Labor senator Katy Gallagher’s bid to stay in parliament has been denied after the High Court ruled that complications with her dual British/Australian citizenship meant that she couldn’t remain a senator.

“I am very disappointed by this outcome but I respect the decision of the Court,” Gallagher said in a statement after the decision was handed down. “To have my place in the Senate end like this today is very deeply disappointing but 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.”

Labor leader Bill Shorten echoed these thoughts, suggesting that Gallagher would return to politics:

“She is too good to lose from public life – and I know we won’t lose her. Katy has a lot more to contribute to Labor and to Australia.”

A new ACT lower house seat was recently proposed by the Australian Electoral Commission as part of a process of redistributing electoral boundaries.

Three other Labor politicians, Susan Lamb, Justine Keay and Josh Wilson, are in a similarly icky dual citizenship scenario, and may now be forced to resign.

This morning, party leader Bill Shorten told the ABC that in the event that the High Court ruled Gallagher ineligible, “we’ll consider what we’ve got to do” with the other three MPs.

#BREAKING: Sky News understands if the High Court rules Labor senator @SenKatyG ineligible to sit in parliament due to her dual citizenship – Josh Wilson, Justine Keay, and Susan Lamb will resign. pic.twitter.com/hAgyVpW7e6

— Sky News Australia (@SkyNewsAust) May 8, 2018

Labor could either send the three remaining politicians to the High Court for cases of their own, or they could encourage them to resign, meaning Labor would suddenly find itself missing four MPs.

If all four MPs are leave Parliament, it will force by-elections in three seats, just weeks after the government handed down a budget full of tax cuts.

Why Are They Being Forced Out?

Section 44 of our constitution says that if you are a citizen of a foreign power (read: another country), you can’t sit in parliament.

Six months ago, seven federal politicians had to defend themselves against claims that they weren’t complying with this part of the constitution — and most of them failed. Of those seven, Scott Ludlam, Larissa Waters, Malcolm Roberts (remember him?), Fiona Nash, and Barnaby Joyce were told they couldn’t sit in parliament.

For Gallagher, things are a little different. She did a bunch of different things to try and renounce her British citizenship before the 2016 cut off date. And she eventually did have it renounced, but she missed the crucial deadline to file her citizenship paperwork.

In that decision six months ago, the High Court decided that a politician was probably in the clear if they took “all steps reasonably required” to revoke foreign citizenship.

But it’s a very, very thin tightrope, as today’s case showed. The High Court told Gallagher that even though she did eventually renounce her citizenship, her actions weren’t good enough. She should have done more.

Her three fellow Labor MPs, as well as Centre Alliance’s Rebecca Sharkie, would likely face a similar decision., which means we’re probably set for four by-elections in the coming months.

But Gallagher might not suffer too much: a new lower house seat in her territory, ACT, just opened up. There’s speculation that the Labor party might just slot her in there as a candidate at the next federal election.