Deputy Greens party leader Larissa Waters resigned on Tuesday after revealing she had held Canadian citizenship since birth. That followed the bombshell resignation of prominent Western Australian Greens Senator and co-deputy Scott Ludlam on Friday, who had held New Zealand citizenship since birth.

"I was devastated to learn that because of 70-year-old Canadian laws I had been a dual citizen from birth, and that Canadian law changed a week after I was born and required me to have actively renounced Canadian citizenship," a tearful Waters told reporters.

Australia's constitution stipulates that a "citizen of a foreign power" is not eligible to be elected to Parliament.

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Ludlam told journalists last week that he was born in New Zealand, but left at age three and had mistakenly thought that becoming a naturalized citizen as a teenager would have replaced his New Zealand citizenship. 

He made light of the situation in a self-depricating Tweet referencing New Zealand slang.

Greens in turmoil

The dual resignations come at a difficult time for the progressive environmental party, which in recent weeks has been plagued with infighting and accusations of bullying.

Senator Lee Rhiannon is facing possible expulsion from the party, ostensibly for lobbying against an education reform bill that needed the support of the Greens to pass, allowing her colleagues to negotiate changes. Respected Greens party elder Bob Brown backed formal complaints against her, and accused her of introducing factionalism into the party.

Rhiannon has tried to push the party back to its left-wing roots, after a drift towards the mainstream in a bid for broader support.

Waters made headlines internationally when she breast-fed in Parliament and was a strong opponent of a proposed and deeply divisive coal mine.

The Greens will likely retain all of their eight Senate seats and their balance-of-power role despite the twin resignations, with the two seats going to other Greens candidates.

Both senators could be forced to repay their parliamentary salaries. Ludlam reportedly earned more than 1.6 million Australian dollars ($1.3 million, 1.1 million euros) during his nine years in office.

Greens leader Richard Di Natale said that he was "gutted" by the loss of his deputies and that the party will tighten procedures to prevent ineligible candidates from running again.

"The Parliament and the nation are worse off as a result of the resignation of two leaders of such integrity and ability as Larissa and Scott," Di Natale said in a statement.

Questions over dual citizenship

More than 20 other MPs currently serving in the Australian Parliament were born overseas, according to Fairfax Media. Last year's census indicated that 28 percent of Australia's population is born abroad. 

In her resignation comments, Waters said she suspected other lawmakers also held dual citizenship. Several members of Parliament shared proof of renounced citizenship, including former Prime Minister Tony Abbott.

Some Australian media commentators have denounced the rule as a relic of the past, saying it made millions of Australians ineligible for Parliament.