Gay rights advocates say they are the underdogs but will campaign hard for a yes vote in the government's same-sex marriage postal survey after losing a High Court challenge against it.
Two groups of advocates on Thursday lost their High Court challenge to the government's $122 million voluntary postal vote on same-sex marriage.
Those who brought the case are disappointed with the outcome but Australian Marriage Equality co-chair and plaintiff Alex Greenwich said they were now focused on a win.
"This is going to be a tough campaign but we are in it to win it," Mr Greenwich told media outside the High Court in Melbourne.
"But certainly the task ahead is daunting and clearly, having had this process imposed upon us in this circumstance, we are clearly the underdog."
LGBTI rights campaigners have questioned the legal validity of the postal plebiscite and its cost, as well as the proposed role of the Australian Bureau of Statistics in the ballot.
Ballots will be sent to voters from next week.
The Coalition for Marriage is pleased parents would be able to have their say about the de-gendering of marriage.
"This is a referendum on freedom of speech, freedom of religion and parents' freedom to have their children free of radical LGBTIQ sex-education which becomes widespread and compulsory in schools after the law changes," spokesman Lyle Shelton said.
Mr Shelton, who is also the managing director of the Australian Christian Lobby, said the coalition would continue to campaign against same-sex marriage until the survey was completed and urged prospective no-voters to donate to their lesser-resourced cause.
