Christian advocacy group FamilyVoice Australia is demanding equal public funding for the yes and no cases to avoid "bullying tactics of rainbow activists" ahead of the postal ballot on same-sex marriage.

"The bullying tactics of rainbow activists ahead of the Irish experience[1] should warn Parliament to fund both cases," said FamilyVoice National Director Ashley Saunders.

"The voters must have the opportunity to consider their verdict with carefully presented reasons for and against same-sex marriage.

"Heavy spending from overseas by same-sex activist sources and bullying tactics in Ireland should not be replicated in Australia.

"Current legislation empowering the Australian Bureau of Statistics should be adequate to include background detail to the question," he said.

"The postal ballot must also be compulsory, just like completing the census, so the result has popular legitimacy."