The likely High Court case about Bob Day's eligibility to be a senator will set a legal precedent that could endanger other politicians' right to sit in Parliament.

Key points: High Court case would revolve around an anti-corruption section of the constitution

High Court case would revolve around an anti-corruption section of the constitution It prohibits parliamentarians from having a relationship with companies getting government contracts

It prohibits parliamentarians from having a relationship with companies getting government contracts Bob Day case could have far-reaching implications for many politicians

The impending case will revolve around an anti-corruption section of the constitution that prohibits parliamentarians from having even an indirect relationship with companies that get government contracts.

But the section is not precise and has never been tested by a full bench of the High Court.

A ruling in the Day case could have far-reaching implications for many politicians.

"Given the possibility for many members to have indirect arrangements with the Commonwealth, I think there may be others who would wonder just how far this can go," Dean of the University of New South Wales Law School George Williams told AM.

"The parties will be keeping a very close look on it because it will affect the sort of candidates they can run at future elections."

The ABC understands legal advice given to the Government suggests Mr Day's electorate office arrangements may have breached the section.

Though the Commonwealth paid no rent for his office space, it does have a lease agreement in place with the owners of the building.

Mr Day used to own the building but sold it to associates after he was elected.

He backed the loan his associates used to pay for the sale, creating the possible constitutional breach.

Labor to support Government's referral

The Senate is likely to be down a senator until at least the end of the year while the High Court decides the matter.

Labor said it will support the Government's plan to next Monday refer the former Family First senator's office arrangements to court.

A replacement for him in the Senate cannot be chosen until the court decides whether or not he was eligible to take a seat in the Senate.

That is expected to take several weeks even if the case is expedited, likely leaving the Senate down to 74 senators for the year's remaining three parliamentary sitting weeks.

The Government had hoped to test its numbers in the Senate during that period by putting several pieces of legislation to it, including one to re-establish the Australian Building and Construction Commission (ABCC).

The ABCC legislation was blocked by the last senate and was a trigger for this year's double dissolution election.

One Nation or Labor could end up with extra Senate seat

There are predictions that One Nation or Labor could end up getting an extra Senate seat if votes need to be recounted after the ruling by the High Court.

The ABC's election analyst, Antony Green, said if Day's election were to be ruled as invalid, he would effectively be erased from the last Senate ballot paper, leaving only one other Family First candidate there.

Green said if there were to be just one candidate on the ballot paper concerned, questions would then arise about whether the party was entitled to have its own group column on the ballot paper.

"If excluded as a column on the ballot paper, the preferences of Family First would be distributed to other parties on the ballot paper as a first choice and the final seat may be won by either Labor or One Nation, based on a recount of that type," he said.