Bill Shorten gave a "rolled gold guarantee" none of his MPs would be caught up in the citizenship crisis, but now he's facing three by-elections and replacing a senator.
In August last year, the opposition leader was adamant.
"We have a strict vetting process. There is no cloud over any of our people," he said.
There are now more Labor MPs forced out of parliament by dual citizenship than coalition members.
After the High Court disqualified Labor senator Katy Gallagher on Wednesday, colleagues Susan Lamb, Josh Wilson and Justine Keay announced they would quit the lower house because they were also British citizens when the 2016 election writs were issued.
Backbencher David Feeney quit earlier this year when he couldn't find evidence he had renounced his British citizenship.
Liberals Stephen Parry and John Alexander and Nationals Barnaby Joyce and Fiona Nash were last year caught out by dual citizenship.
Mr Shorten faced tough questioning on Wednesday over his insistence that his MPs would be fine, saying he acted in good faith, following the advice from the party's lawyers.
"If you get your lawyers, you do take their advice, it's been the same advice for 20 years," he told reporters on Wednesday.
"They said our position was sound."
Mr Shorten said Labor relied on legal advice that said if candidates took "all reasonable steps" to renounce their citizenship then they would be eligible to sit in parliament.
All three MPs said they intended to run again in by elections expected in June.
But Ms Lamb still hasn't renounced her British citizenship, which means she's been claiming her parliamentary salary for more than six months while knowing she was breaching the rules.
"She's going to renounce her citizenship," Mr Shorten said.
"I'm confident now we've seen the decision Susan will be eligible to nominate for Parliament in the very near future."
But he admitted he didn't know whether she had the copy of her parents' marriage certificate she needs to renounce her citizenship.
"I'm not aware of each piece of paper." he said.
After making political mileage when four coalition members were caught out as dual citizens last year, Mr Shorten refused to accept responsibility for his party's woes on Wednesday.
"It seems that rolled gold process Bill Shorten was boasting about arrogantly some time ago isn't so rolled gold after all," Treasurer Scott Morrison said at a National Press Club event.