There is disagreement among Coalition opponents of same-sex marriage over whether religious freedoms caused by changing the Marriage Act should be detailed up-front.

Former prime ministers John Howard and Tony Abbott are leading the No campaign's calls for the Government to detail what steps it will take to protect religious freedoms if the Yes campaign prevails.

But Treasurer Scott Morrison — who is also opposed to change — was yesterday insisting those details only needed to be sorted out if the majority of Australians replied yes in the postal survey.

"That is the process. That was going to be the process under the previous compulsory attendance plebiscite, that was exactly what was put to the Parliament," he told Sky News.

"So the only difference in method here is it is being done through a non-compulsory survey."

His comments have drawn criticism from Liberal senator Eric Abetz , who believed the Treasurer was asking Australians to have blind faith in Parliament.

"Well the Treasurer has basically said 'if you vote yes, you can trust us to protect religious freedoms'," he said.

"I'm not as trusting of politicians as the Treasurer is ... there are consequences that flow, but they go a lot lot further than just people of a religious expression, it's it's about freedom of speech, parental rights, and the rights to be a conscientious objector without religious disposition.

"The simple fact is nobody knows what the protections are and will be or how far they will go, and in all those circumstances the Australian people should not be buying a pig in the poke or giving the Parliament a blank cheque."

Religious protections 'absolutely necessary'

Key dates in SSM postal survey: August 24 — the final day to register with the AEC if you want to take part in the survey

September 12 — survey forms start being sent out

September 25 — all forms are expected to have been sent

October 27 — forms are strongly encouraged to be returned by this date

November 7 — the final deadline to return surveys

November 15 — results are released

While the Treasurer defended the Government's decision not to release legislation unless a majority of Australians replied yes in the postal survey, he said he felt strongly about including religious protections if a bill was introduced.

"If it were to return a yes then it would be absolutely necessary to ensure that religious freedoms were protected and as a member of the Parliament I would be very forward leaning to ensure that that occurred," he said.

"The freedom of religion more generally is something I feel very strongly about and is one of the reasons I have been fairly active on this issue in the past.

"If the survey were to return a yes, well any bill that would then come forward, the Prime Minister has made this point, he would be working very hard to ensure religious freedoms were protected and I can assure Australians this would be at the top of my list for that particular bill and how it went through."