The Greens are seeking fresh legal advice about the eligibility of their newly installed Senator Andrew Bartlett.

They have taken the move because of what they call the unexpected ruling yesterday by the High Court that Liberal Hollie Hughes could not replace former Nationals senator Fiona Nash.

Key points: Bartlett rejects eligibility concerns over contract he had with ANU

Concerns came after High Court struck out Liberal Hollie Hughes over government role

Man set to replace Lambie in Senate could also be ineligible

The court struck out Ms Hughes under part of the Constitution that says parliamentarians can not hold a government job.

Senator Bartlett had a contract with the Australian National University when he nominated as second candidate on the Queensland Greens ticket last year.

But he insisted Wednesday's decision had "no relation to my situation".

"The ruling regarding Hollie Hughes is an entirely different matter and bears no relevance to my situation or anybody else's," he told the ABC.

The former Democrats leader argued university work was not an "office of profit under the crown", as set out in the Constitution.

"The legal advice I've received repeatedly over many years … is very consistent, that working for a university has never been found to be an office of profit under the crown," he said.

"The High Court was fully aware I worked for a university at the time they chose to declare me elected to the Senate."

But the Greens have today decided to ask for more advice about his eligibility because of the nature of yesterday's High Court ruling.

Senator Bartlett was declared elected by the High Court last week, replacing former Queensland senator Larissa Waters — the second politician to fall during Parliament's citizenship saga.

The court heard there might be an "issue" with his qualification, but allowed him back into the Upper House anyway.

High Court applying disqualification provisions 'strictly'

The High Court yesterday considered whether next in line on the New South Wales Coalition Senate ticket, Ms Hughes, would replace Senator Nash.

The Turnbull Government gave Ms Hughes a plum job with the Administrative Appeals Tribunal in June this year, worth at least $179,000 a year.

Ms Hughes was not employed by the Government during last year's election campaign, or at Friday's recount.

But the court ruled because Ms Nash was ineligible last July, the 2016 election was technically ongoing until the recount was completed.

"I am obviously disappointed, but I respect the High Court's decision. I was looking forward to representing the needs of rural and regional families, particularly those who have kids with special needs," Ms Hughes said in a statement.

"I will continue my advocacy on their behalf with the Country Autism Network, as well as through my board positions on StreetWork and the Critical Window Foundation. I will also continue my work on behalf of rural and regional Liberal members and supporters, continuing to promote the needs of country communities," she said.

Sydney University constitutional law expert Anne Twomey said Wednesday's ruling again showed the court was interpreting the 116-year-old founding document "very, very strictly".

"This is really sending out a very loud message to members of Parliament that the High Court will apply those disqualification provisions strictly," Professor Twomey said.

The respected academic previously said the status of university employees was unclear, and said eligibility could vary depending on the institution.

Fellow constitutional law professor George Williams yesterday tweeted: "Surely Andrew Bartlett will now be referred to the High Court."

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Both academics also agree that the Tasmanian man set to replace Jacqui Lambie in the Senate could also be ineligible.

Steve Martin was second on the Jacqui Lambie Network Senate ticket at the last election but is the Mayor of Devonport.

It is possible the mayoral role constitutes an 'office of profit under the crown' under the Constitution, which would disqualify him.

Mr Martin was expected to announce his decision whether to contest the re-count today, but a joint press conference with Ms Lambie has been cancelled.

He received advice from former Senate clerk Rosemary Laing when he stood for election last year, which found that it was unlikely the office of mayor would be found to be an office of profit under the crown under section 44 of the constitution.

"This is because councillors are elected by the electors, they are not appointed by the executive government and payments made to them are determined by statutory entitlements in respect of their offices," Ms Laing wrote to him.

Professor Williams said Mr Martin's case should be sent to the High Court as a test case.

He argued the issue needed to be resolved.

"Either the High Court itself could seek to resolve it as they did for the Hollie Hughes issue, or it could be referred by the Senate," Professor Williams said.