A day after the same-sex marriage postal vote was approved by the federal government the High Court has received two applications to stop it from happening.
The first was lodged in Sydney on Thursday afternoon by the Public Interest Advocacy Centre on behalf of Tasmanian independent MP Andrew Wilkie, advocate Felicity Marlowe and the Parents and Friends of Lesbians and Gay.
The Human Rights Law Centre followed with its own application made on behalf of Australian Marriage Equality and Greens Senator Janet Rice in Melbourne.
It's unclear at this stage if the cases will be joined.
Both applications question the legal validity of the postal plebiscite and argue the expenditure of $122 million for the vote is not constitutionally valid because it hasn't been approved by parliament.
"It is crucial that we launch these proceedings and confirm the legal validity of the postal plebiscite before $122 million of taxpayer dollars is spent on an unfair and unnecessary process only designed to frustrate and delay marriage equality," HRLC legal advocacy director Anna Brown said in a statement on Thursday.
Same-sex advocates argue Finance Minister Mathias Cormann didn't have the authority to make the allocation of funds without parliamentary approval with PIAC chief executive Jonathan Hunyor saying "the power the finance minister is purporting to exercise is one that itself needs to be tested".
Ms Brown says, under the Appropriation Act, Mr Cormann can only seek an advancement of funds in urgent and unforeseen circumstances.
"It's difficult to see how the fulfilment of an election commitment is unforeseen," Ms Brown said.
PIAC will also argue the commonwealth doesn't have the power to authorise the postal plebiscite and the Australian Bureau of Statistics can't run the vote on gay marriage.
"The exercise simply isn't a statistical one and so it doesn't fall into the power of the ABS which has a job relating to statistics," Mr Hunyor told reporters in Sydney.
"We will be arguing that by going ahead without the authorisation of parliament the government is acting beyond its power.
"The government cannot validly undertake a postal vote and also that it cannot fund the exercise without parliamentary approval."
Prime Minister Malcolm Turnbull insists if the postal ballot is blocked by the High Court there'll be no further action on same-sex marriage.
The government was forced to adopt the postal vote on same-sex marriage after the Senate rejected a second bid for a compulsory plebiscite.
PIAC is seeking to have the matter heard urgently in the High Court as postal vote ballot papers are due to hit mailboxes from September 12.
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