Ballarat MP Catherine King has taken aim marriage equality opponents, including government MP Tony Abbott, in a fiery Facebook post.
Ms King posted a picture of her parliamentary office in Canberra decorated with coloured love hearts.
She challenged Mr Abbott personally, saying “marriage equality was the right thing to do now” in the post.
The federal government announced it would use the Australian Bureau of Statistics to launch a postal vote on the issue in September.
However large sections of the community, who are overseas or have no fixed address, have been left with no way to take part.
Ms King said she had wanted to make a statement in support of equality.
“It has been a pretty emotional week in Parliament, but nothing compared to what it has been for many in the LGBTQI community who are desperately hoping parliament will resolve this issue,” she said.
“A lot of people think this has gotten beyond the Parliament doing its job.
“We are elected to do a job – I am on the record as being a supporter of same sex marriage for some time now.”
Ms King said she addressed Mr Abbott personally because she is next to his parliamentary office.
The government twice tried to pass legislation for a formal plebiscite run by the Australian Electoral Commission, but failed both times.
There is now doubt about the ability of the ABS to enforce the usual campaign rules prohibiting deceptive or misleading information.
Prime Minister Malcolm Turnbull has also said, while campaigning for a republic in the 90s, that a postal vote disenfranchises voters.
The opposition has confirmed it will back the yes campaign, despite its reservations about a postal vote.
However there is also nothing requiring MPs from either side of the debate to back the majority vote.
Meanwhile the Ballarat Pride Hub has started a campaign to encourage people to vote yes.
Spokesperson Kirsten Holden said the group was buoyed by Ms King’s support.
“Catherine has always been amazingly supportive of our LGBTIQ community and we couldn't be happier to have her on board,” she said.
The pride hub’s Facebook post said the group wanted as many yes votes as possible on the ballots.