The High Court may be putting another federal politician under the microscope but this time it has nothing to do with citizenship.

Key points: Assistant Health Minister fighting attempts to have his business interests scrutinised

Assistant Health Minister fighting attempts to have his business interests scrutinised David Gillespie owns a shopping centre in Port Macquarie, one of the tenants is an Australia Post franchise

David Gillespie owns a shopping centre in Port Macquarie, one of the tenants is an Australia Post franchise Labor wants to know whether that breaches ban on deriving financial interest from Commonwealth

Assistant Health Minister David Gillespie is fighting attempts to have his business interests scrutinised for whether they breach the constitution.

Dr Gillespie owns a shopping centre in Port Macquarie, and one of the tenants is an Australia Post franchise.

The man he defeated in his electorate of Lyne at the 2016 election, Labor's Peter Alley is trying to get the High Court to decide whether that breaches the constitution's ban on elected officials deriving any financial interest from the Commonwealth.

The usual process for the High Court to consider eligibility questions is by a formal referral from parliament.

But that has not happened in this case, so Mr Alley first has to prove he has sufficient legal standing to bring the case and argue the High Court has the power to hear the arguments.

He is claiming the eligibility crisis currently gripping Parliament heightens the need to hear the case, and relying on Parliament to refer a Government Lower House MP to the High Court is unlikely to happen because the Coalition controls the numbers.

Lawyers for Dr Gillespie maintain the Parliament should have the responsibility for deciding whether there are questions to answer.

Mr Alley is trying to frame it as a similar case to that of former South Australian senator Bob Day.

In April, the High Court ruled Mr Day was ineligible to hold office because of an indirect financial interest in a property leased to the Commonwealth, that he used for his electorate office in Adelaide.

The current case is complicated because Dr Gillespie's tenant is a licenced post office (LPO), which is effectively a franchise.

That means there is no direct financial link to the Commonwealth.

But the wording of section 44(5) of the constitution could still catch the Assistant Minister:

Any person who: (v) has any direct or indirect pecuniary interest in any agreement with the Public Service of the Commonwealth otherwise than as a member and in common with the other members of an incorporated company consisting of more than twenty-five persons; shall be incapable of being chosen or of sitting as a senator or a member of the House of Representatives.

The Full Court will hear the case in Canberra today.