Political conservatives who support same-sex marriage have launched a campaign to convince voters to say 'yes' in the upcoming postal survey.
The campaign features messages from Liberal and Nationals party elders - including federal cabinet ministers Christopher Pyne and Kelly O'Dwyer, Tasmanian Premier Will Hodgman, and former Victorian premier Jeff Kennett - as well as voters and party members.
"There is a very strong case for same-sex marriage within the liberal and conservative traditions embodied by the Liberal party," spokesman Luke Barnes said.
That was reflected in support among party members and politicians as well as growing support within the Nationals.
But Treasurer Scott Morrison isn't amongst them, telling reporters in Canberra he will be voting 'no'.
Asked if he will be campaigning he said: "I've got a pretty important job to do as treasurer and I'm focused on the nation's finances".
"But I respect the views of everybody else as an advocate for ensuring that all Australians have their say."
Meanwhile, polling commissioned by same-sex marriage advocates found two-thirds of Catholic Australians say they'll vote yes - broadly in line with polling for the wider community.
The proportions were similar for Australians from other religions, the Newgate Research poll found.
"The upper management of the (Catholic) Church isn't listening to the flock who have made up their minds on marriage equality because it's about their friends, family members and neighbours," Equality Campaign executive director Tiernan Brady said.
"This is about civil marriage, not religious marriage. Allowing lesbian and gay couples to have access to civil marriage will not interfere in any way with any religious sacrament and nor should it."
A record proportion of Australians have enrolled to vote after a push from both sides of the marriage campaign to encourage people to take part.
The Australian Bureau of Statistics will run the voluntary postal survey with ballot papers set to arrive in letter boxes from mid-September, pending the outcome of a High Court challenge.