AUSTRALIANS should prepare for an early election as Malcolm Turnbull considers all options to rescue his struggling government.

The sustainability of the Coalition is now in doubt with as many as five Nationals MPs and senators facing rulings they were ineligible to sit in Parliament.

If disqualified, it would mean a quarter of Nationals in Parliament were, unintentionally, there under false pretences.

Labor will continue to demand all frontbench MPs and senators whose status is being challenged quit the ministry until matters are resolved.

"This is a government in chaos. This is a government clinging on to power," said Opposition Leader Bill Shorten.

The constitutional challenges have smashed the Nationals' confidence and the capacity of its leadership to contribute to govern, and added substantial instability to the Turnbull administration.

Those at risk include party leader and Deputy Prime Minister Barnaby Joyce and party deputy leader Fiona Nash. Former Resources Minister Matt Canavan has surrender his frontbench job and his vote in the Senate as he waits to have his eligibility tested by the High Court.

All three could be casualties to the constitutional ban on dual citizenship - Mr Joyce New Zealand, Senator Nash British, Senator Canavan Italian.

Further, two Nationals have been identified for possible disqualification under a constitutional ban on candidates who have an office of profit under the Crown - in short, for having business links with government.

They are Queensland Senator Barry O'Sullivan and member for Lyne David Gillespie.

The next scheduled election will be held between late next year and late 2019. This is complicated by elections in Queensland, Victoria and NSW in that period.

The High Court has been asked to rule on the cases but might not be able to do that until October or possibly even November.

Mr Turnbull might not be able to stonewall for that long as his MPs are hit with challenges to their qualifications.

He could decide to hold a referendum on the restrictions on eligibility of candidates at the same time as an election.