01/11/2016 7:03 PM AEDT | Updated 01/11/2016 10:50 PM AEDT

Federal Government Calls On Senators To Challenge Bob Day's Election Validity

The matter could be referred to the High Court.

Bob Day resigned in October, and his senate spot is due to be filled.

In a move that could have far-reaching consequences for the Government's fragile hold on the Senate, the Federal Government will ask senators to refer information concerning Family First senator Bob Day's election validity to the High Court.

On Tuesday evening, Attorney-General George Brandis and Special Minister of State Scott Ryan released a statement announcing that Ryan has written to the President of the Senate, Stephen Parry, concerning Day's senate spot.

According to Fairfax, Parry emailed senators late on Tuesday afternoon about Day's position, confirming he was "considering information which raises difficult constitutional questions relating to the composition of the Senate and I am seeking further advice".

Day made the decision to resign from the Senate in October after his construction business went into liquidation. Then, earlier on Tuesday, he announced his resignation "effective immediately".

Following standard procedure, Day would be replaced by another Family First senator, which would be approved by the South Australian Parliament.

Brandis and Ryan identified a possible "indirect pecuniary interest" as their reason for questioning the Senator's election validity.

"The information relates to s44(v) of the Constitution, regarding a potential indirect pecuniary interest in a contract with the Commonwealth," the statement read.

"When the Senate reconvenes on Monday 7 November the Government intends to initiate a Senate referral of the matter to the High Court pursuant to s376 of the Commonwealth Electoral Act."

Of the crossbench, the Family First senator is the most closely aligned with the Government's policies and is crucial to the Turnbull Government's ability to pass legislation through the Senate.

If Senator Bob Day's election is proved to be invalid, it would prompt a recount of all South Australian Senate votes from the July 2 election. This could result in the election of another crossbencher or even a member of the Labor party, altering the makeup of the Senate and creating fresh challenges for the Government in passing legislation.

On Tuesday night, Family First released a statement confirming the party is seeking legal advice.

"Family First has today been made aware of allegations of a potential indirect pecuniary interest by Mr Bob Day with respect to a contract with the Commonwealth," the statement said.

"Family First has had no prior knowledge of these allegations and Mr Day has denied that any pecuniary interest exists or had existed."

Later on Tuesday evening, Labor Senator Penny Wong released a statement saying that the Labor Party was taking legal advise on whether to refer the matter to the High Court.

"We will take a principled approach by seeking to ensure that the situation is resolved in accordance with the Constitution and electoral laws, that the outcome reflects the democratic will of SA voters and that the matter is dealt with transparently and openly," Wong said in a statement.