Labor has demanded that the Australian Federal Police (AFP) investigate Attorney-General Christian Porter, alleging that he sought to interfere in a Liberal preselection contest.

Key points: Shadow Attorney-General Mark Dreyfus said the AFP need to investigate the appointment of a Liberal preselection candidate to the AAT

Shadow Attorney-General Mark Dreyfus said the AFP need to investigate the appointment of a Liberal preselection candidate to the AAT Jane Bell was appointed to the tribunal days before losing preselection in the Melbourne seat of Higgins

Jane Bell was appointed to the tribunal days before losing preselection in the Melbourne seat of Higgins Christian Porter labelled the claims spurious, and said an investigation would be a waste of the AFP's time

But Mr Porter returned fire on the Federal Opposition, saying its calls for an investigation were spurious and a waste of the agency's time and resources.

Shadow Attorney-General Mark Dreyfus wrote to AFP Commissioner Andrew Colvin, suggesting the police look into Mr Porter's appointment of Melbourne lawyer Jane Bell as a part-time member of the Administrative Appeals Tribunal.

Ms Bell nominated for Liberal party preselection in Higgins in the wake of Minister Kelly O'Dwyer's shock resignation from Parliament.

Her appointment to the AAT was announced just days before she lost preselection to Melbourne doctor Katie Allen.

"The timing of Mr Porter's appointment of Ms Bell to the AAT was curious," Mr Dreyfus wrote to Mr Colvin.

"The Attorney-General's decision to offer Ms Bell a position on the AAT at the same time as she was seeking endorsement to stand as a candidate for election to the Federal Parliament is highly questionable.

"In particular, it raises the question of whether the decision to appoint Ms Bell to the AAT was intended to influence her preselection campaign — or even her decision to seek preselection in the first place."

The demands for an investigation are the latest plank of Labor's attacks on the Government for political appointments to tribunals such as the AAT, and to diplomatic postings.

Mr Porter said the latest accusations levelled against him by his counterpart were an example of political overreach, and said Ms Bell's decades in the legal profession made her "excellently qualified" for the AAT.

"Ms Bell's appointment was finalised before her nomination for preselection for Higgins," he said.

"Had she won that preselection, she would no doubt had to have resigned her position on the AAT.

"It is impossible to link her appointment to the AAT to preselection, because at the time of her appointment her future nomination was entirely unknown."

Ms Bell was one of eight candidates for preselection in Higgins but was rarely mentioned as a likely successor to Ms O'Dwyer.

Government sources said the AAT appointments were taken to Cabinet in early January, well before Ms O'Dwyer announced she would not contest the 2019 election to spend more time with her family.

Illegal to use inducements to influence political candidates

Labor alleged Mr Porter's behaviour could be a breach of the Commonwealth Electoral Act.

The Act makes it illegal for an individual to offer any sort of inducement that might influence a political candidate.

Mr Dreyfus has linked the case to that of former Liberal candidate Hollie Hughes, who accepted an AAT appointment after missing out on a New South Wales Senate seat in the 2016 federal election.

The High Court ruled that AAT role precluded her from being appointed to the Senate to replace former Nationals deputy leader Fiona Nash, who was kicked out of Parliament during the dual citizenship fiasco.

But that appointment of Ms Hughes to the AAT happened after the election, and after the closure of nominations for the poll — a date that will only be set for the 2019 ballot after the Prime Minister calls the election.