In a day of high drama, three Labor MPs and a crossbencher have resigned from parliament, and a Labor Senator was kicked out by the High Court, over the dual citizenship saga.

It means there’ll be five by-elections, with the retirement of Western Australian MP, Tim Hammond, last week.

The High Court decision, that Katy Gallagher was a dual British citizenship, and ineligible to be in the Senate, sparked an amazing couple of hours.

Labor member for Longman Susan Lamb making a statement on her citizenship status in the House of Representatives at Parliament House. (AAP) (AAP)

Like dominoes, the others, all under identical citizenship clouds, fell by the way.

The first was South Australian crossbencher, Rebekha Sharkie, who announced at 12.45pm, that given the High Court judgement, she would resign, and contest the resulting by-election.

Under enormous pressure from the government to resign, the three Labor members followed.

Centre Alliance MP Rebekha Sharkie has also resigned. (AAP) (AAP)

Within minutes, Tasmania’s Justine Keay, rose in the House of Reps, to resign.

She was followed by WA’s Josh Wilson, then Queensland’s Susan Lamb.

All three said they’ll re-contest their seats.

All were defiant.

“I am not done yet,” Ms Lamb said.

“This is not a valedictory speech. I intend to be back.”

The drama had become a major embarrassment for Opposition Leader Bill Shorten, who had insisted Labor had “rolled gold” vetting procedures, and his MPs were eligible to be in parliament.

The by-elections will be problematic for the Labor Party.

Labor MP Josh Wilson reacts as Australian Treasurer Scott Morrison introduces the Personal Income Tax Bill today. (AAP) (AAP)

Mr Wilson’s seat of Fremantle will come under threat from the Greens, Justine Keays’ seat of Braddon is marginal, so too, Ms Lamb’s seat of Longman.

Ms Sharkie’s seat of Mayo was a Liberal stronghold and is considered shaky.

The whole citizenship sage has claimed 15 MPs and Senators, including former Deputy Prime Minister Barnaby Joyce.

The former Nationals leader said he had no sympathy for the MPs because they didn't resigned when he did.



"We gave the opportunity then, but remember Tony Burke and the Labor party they thought it was great sport, every day," he told Sky News today.



"They said that I was not entitled to be there.

"We put it to them they had people on their own side in the same predicament and now that predicament has come to be the fact."

The resignations of the MPs will take effect on Friday.

Labor member for Braddon Justine Keay during Question Time in the House of Representatives at Parliament House in Canberra. (AAP) (AAP)

Mr Shorten defended his refusal to act earlier, saying the High Court had set a new precedent.

“The High Court has set a stricter test and we accept that,” he said.

“In good faith, we relied on the same advice for 20 years. At all times the Labor Party has acted in good faith.

“These are the facts and we have to deal with it. We followed the legal advice we’ve been given.”

And, he said, in the wake of previous rulings, the party had the legal advice re-checked.

He was confident Susan Lamb will have her British citizenship renounced in time to re-contest the Sunshine Coast seat.

“She will be eligible to nominate," he said.