(This August 17 story has been corrected to make clear that Australians with dual citizenship are prevented from being elected to parliament in paragraph 1)

MELBOURNE (Reuters) - An Australian senator on Thursday became the sixth politician to have their eligibility to sit in parliament questioned over dual citizenship rules, which proscribe Australians who are dual citizens from being elected to parliament.

Fiona Nash, deputy leader of the National Party, the minor party in the ruling coalition, told the Senate she was a dual British citizen.

The one-seat majority of the Liberal-National government would not be threatened if Nash were forced to step down because the Nationals would retain her seat in the Senate.

But the revelation is likely to be an embarrassment for the government which has criticized other parties for not checking thoroughly the status of members.

Deputy Prime Minister Barnaby Joyce, also from the National Party, said on Monday he may not be eligible to be in parliament after being told he may be a dual citizen of Australia and New Zealand.

New Zealand later said Joyce held citizenship as his father was born there. His mother was Australian and his father came to Australia in 1947 as a British subject.

Joyce said he would not resign or temporarily step down from office after being told by Australian Solicitor-General Stephen Donaghue that he would likely be cleared by the High Court.

“The legal advice is exactly the same as Barnaby Joyce’s,” Nash’s spokesman told Reuters.

“It says that section 44 doesn’t apply to her because she didn’t take citizenship herself and had no reasonable knowledge.”

Nash’s estranged father, who was British, died a decade ago.

Prime Minister Malcolm Turnbull said on Monday he was confident his government’s slim majority was safe, despite the questions over Joyce’s citizenship, which could disqualify him from parliament.

Australians are not eligible to be elected to parliament if they hold dual or plural citizenship.

The High Court will begin hearings into Joyce’s eligibility on Aug. 24. Should he be ruled ineligible, Turnbull would be forced to rely on independents to pass legislation.