The parties to the challenge, which could be lodged as early as Wednesday, include Tasmanian independent federal MP Andrew Wilkie and marriage equality advocates Shelley Argent and Felicity Marlowe.
The Turnbull government has proposed the Australian Bureau of Statistics run the postal vote, which will start in mid-September unless a court injuncts it.
However, long-term same-sex rights advocate Rodney Croome said legal advice provided by barrister Ron Merkel QC found there were constitutional problems with the ABS running the poll.
"Mr Merkel feels that the idea of a postal vote running through the ABS may exceed the ABS's authority, particularly when we consider whether a postal vote on marriage equality is statistic gathering or not," Mr Croome said.
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'It's exposing our children to hatred': Wong calls for rethink on same-sex marriage plebiscite
Labor senate leader Penny Wong has slammed the Australian Christian Lobby for likening children of same-sex couples to ‘the stolen generation’.
It comes after the Senate has blocked a government move to restore the same-sex marriageplebiscite to its agenda following an emotional debate.
Labor, the Greens and the Nick Xenophon Team on Wednesday had the numbers to tie a vote at 31-all, meaning the move was defeated.
Liberal backbencher Dean Smith, whose attempt to initiate a parliamentary vote on gay marriage was stymied by his party colleagues this week, supported the government but chose to sit with the crossbench.
'It's not a unifying moment': Senator Wong slams Cormann on plebiscite vote
