The fallout over MPs' citizenship rights in foreign countries has widened to engulf more than 20 federal politicians, placing Prime Minister Malcolm Turnbull’s majority government under threat.

Investigations are today underway to determine whether Victorian Liberal MP Julia Banks holds Greek citizenship.

The liberal backbencher was born in Melbourne to parents of Greek heritage.

But she said she has never taken up Greek citizenship, as speculation swirls around her heritage status.

Ms Banks is added to a list of twenty-one other members of the House of Representatives who have spoken of their migrant bloodlines - many during their maiden speeches - The Australian reported.

They include frontbenchers from both the Coalition and Labor such as Deputy Prime Minister Barnaby Joyce, Trade Minister Steven Ciobo, Liberal MP Julia Banks, deputy Labor leader Tanya Pilbersek and Labor MP Steve Georganas.

Deputy PM Barnaby Joyce has New Zealand heritage.

The resignation from the cabinet of Nationals senator Matt Canavan, after it was revealed he had gained Italian citizenship without being born in, or visiting the country, has shown how vulnerable MPs who could be entitled to foreign citizenship are.

Now MPs such as Joyce, whose father was born in New Zealand and Ms Banks, whose father was born in Greece, face scrutiny over their family heritage.

With speculation over Ms Banks’ Greek heritage, the federal government is bracing for wider political ramifications.

The Coalition holds a one-seat majority in the House of Representatives which bans anyone who is a “citizen or entitled to the rights or privileges of a subject or a citizen of a foreign power”.

The High Court could be asked to determine if Ms Banks’ entitlement to Greek citizenship makes her ineligible, and to rule on whether she should have renounced any citizenship entitlements before nominating.

A disqualification of a member in the lower house would likely lead to a by-election and put a big cloud over the future of the government.

Last night, One Nation Senator Malcolm Roberts became the latest federal politician to become embroiled in the citizenship furore.

He said he did not receive confirmation he had renounced British citizenship until months after the federal election, but is confident of surviving any challenge to his eligibility.

Labor deputy leader Tanya Pilbersek is one of the 20 MPs.

Senator Roberts said he wrote to British officials on May 1 last year asking if he was a UK citizen, given he was born to a Welsh father in India.

He had no reason to believe he was British, but thought it best to double-check while filling out a nomination form for the Senate.

Five weeks later he hadn't received a response, so wrote again on June 6 - three days before nominations closed - saying that if he had British citizenship, he fully renounced it.