The disqualification of a Labor Senator caught up in the dual-citizenship debacle has led to the resignations of four other federal MPs.

The High Court has ruled Katy Gallagher breached the constitution for holding foreign ties at the time of the last election.

Senator Gallagher argued she took all reasonable steps to renounce her foreign status before the closure of nominations for the 2016 federal poll, despite the Commonwealth claiming she left her run too late.

Opposition MPs Susan Lamb, Justine Keay and Josh Wilson have been facing similar questions over their eligibility and have decided to quit.

Independent Rebekha Sharkie has also stepped down.

The resignations will spark four by-elections. They will all stand for re-election.

BREAKING: ALL THREE Labor MP’s under a citizenship cloud are resigning.

Centre Alliance MP Rebekha Sharkie has also stepped down.

That’s four resignations within 3 hours of the High Court’s decision on Labor Senator Katy Gallagher.@2GB873 @3AW693 @NewsTalk4BC @6PR

— Eliza Edwards (@ElizaEdNews) May 9, 2018