Even the barest of majorities for the yes vote on the same-sex marriage survey will be enough for the Turnbull government to push for the law to be changed.
Prime Minister Malcolm Turnbull says the government will facilitate a private members' bill to legalise same-sex marriage if the yes vote garners more than 50 per cent.
"That's democracy. A majority is a majority whether it's a big majority or a little one," Mr Turnbull told KIIS FM Radio.
Mr Turnbull said neither voter turnout nor how narrow the margin was would affect the government's position.
"I'd be delighted to see a yes vote and I'd be especially pleased to see a high participation," he said.
Yes and no campaigners could face a fines of up to $12,600 if their material includes hate speech or they engage in bribery.
The government on Tuesday night finalised a deal with Labor to pass protections - to be introduced to the Senate on Wednesday - governing the conduct of the survey campaign.
The bill, expected to pass parliament this week, would make it an offence to vilify, intimidate or threaten to cause harm to a person on the basis of their sexual orientation, gender identity, intersex status or religious conviction during the survey.
Finance Minister Mathias Cormann said there were also provisions for authorisation of advertisements, reasonable opportunity to have opposing views broadcast, offences against bribery and threats and the prohibition of misleading and deceptive conduct in relation to the completion of survey forms.
"We want this process to be fair and for Australians to get the opportunity to have their say in an appropriate environment," Senator Cormann said.
The legislation would be in effect for the period between its commencement and the declaration of a result on November 15.
The Australian Bureau of Statistics is aiming to get the survey forms out to 16 million voters by September 25, with the first forms in mailboxes this week.
The form asks, "Should the law be changed to allow same-sex couples to marry?", followed by yes and no boxes to be marked.