Federal MP David Gillespie has sold off the regional post office that threatened his political career - and the Turnbull government's parliamentary majority - paving the way for him to run in a possible byelection.

Labor has launched a High Court challenge against the Nationals MP, who serves as Prime Minister Malcolm Turnbull's assistant health minister, because it believes the Australia Post outlet could be an indirect financial interest in the Commonwealth – grounds for disqualification under section 44(v) of the constitution.

As revealed by Fairfax Media a year ago, Dr Gillespie owns a small suburban shopping complex in Port Macquarie on the NSW north coast and one of the shops was being leased to a franchisee of Australia Post – a government-owned corporation.

But Dr Gillespie updated his pecuniary last week to reveal he had sold the shop in recent weeks.