The future of Australia's deputy prime minister Barnaby Joyce was in doubt on Monday when he revealed he may not be eligible for parliament after being informed he may be a dual citizen of Australia and New Zealand.
Australian politicians are not eligible to be elected to parliament if they are hold dual or plural citizenship, a rule that has forced the resignation of two senators in recent weeks.
Mr Joyce said he was informed by New Zealand officials last week that he may be a citizen by descent.
While he was born in Australia, his father was from New Zealand and came to Australia in 1947 as a British subject. His mother was Australian.
"Neither I nor my parents have ever had any reason to believe that I may be a citizen of any other country," he said on Monday.
He said he was fifth lawmaker to be referred to the High Court since last month for scrutiny over whether he was entitled to remain in parliament.
The 116-year-old section of the constitution that bans dual nationals is taking an extraordinary toll on the finely balanced parliament elected in July last year.
The crisis began in July when the minor Greens party's co-deputy leader Scott Ludlam resigned after revealing he had dual Australian-New Zealand citizenship.
Other victims include Canadian-born Greens senator Larissa Waters and resources minister Matt Canavan, who left cabinet after finding his mother signed him up to Italian citizenship in his 20s.
Mr Joyce has asked for the matter to be referred to the Australia's high court for a ruling on his eligibility.
Critics of the constitutional rule argue it no longer suits the modern multicultural Australia in which almost half the population was born overseas or has at least one overseas-born parent.
If Mr Joyce was disqualified, prime minister Malcolm Turnbull's centre-right government could lose its single-seat majority in the House of Representatives where parties need a majority to govern. The other four lawmakers are senators who if disqualified would be replaced by members of their own parties.
* reporting from agencies
