The Turnbull government’s wafer-thin majority is facing a new threat, with Labor launching a High Court challenge against a coalition frontbench MP.

The ALP’s national executive met on Friday to consider a challenge to Nationals MP for Lyne and Assistant Health Minister David Gillespie’s eligibility to sit in Parliament.

A legal bid will now be launched by Labor’s former candidate for Lyne Peter Alley.

Dr Gillespie owns a suburban shopping complex in Port Macquarie, but one of the shops in the complex is an outlet of Australia Post, a government-owned corporation.

Labor has raised questions about the arrangement in the light of the High Court’s disqualification of former Family First senator Bob Day over an electorate office leasing deal with the government.

Under Section 44 of the constitution, anyone with a “direct or indirect pecuniary interest” in an agreement with the commonwealth is disqualified to sit as an MP.

Dr Gillespie’s seat of Lyne was previously held by Independent Rob Oakeshott. Photo: AAP

Dr Gillespie has received independent legal advice that there is no constitutional issue with him sitting in parliament, which the government is satisfied with.

The Nationals would be reasonably placed to retain Dr Gillespie’s seat if a by-election were called, but the kerfuffle would prove an unwanted headache for the government.

A spokesman for Dr Gillespie told The New Daily: “As the matter is now the subject of legal proceedings, it would be in appropriate to make any any comment.”

Labor Deputy Leader Tanya Plibersek said on Friday that Dr Gillespie’s “conflict of interest” had been a matter on the public record since February.

“We are not sure whether Dr Gillespie is actually constitutionally able to sit in the House of Representatives, whether he was properly elected, because of his conflict of interest,” she said.

Ms Plibersek said Labor had previously asked the Attorney-General George Brandis to investigate.

Foreign Minister Julie Bishop described the move as “another Labor stunt” on Friday.

Constitutional law expert Anne Twomey said it was “more likely than not” that the arrangement would be allowed under law.

“Thing is, you can never tell with the High Court,” she told Sky News.

“The High Court has been quite strict in relation to these disqualifications provisions because rightly they it is very important to make sure for democratic reasons that we have people in Parliament that who aren’t the subject of undue influence.

-with AAP