And Mr Dreyfus has suggested a 50 per cent turnout would be a good result for the non-compulsory vote, while urging Prime Minister Malcolm Turnbull to "put a bit of his shoulder to the wheel here" and campaign for a 'yes' vote.

The High Court will consider two similar challenges - one brought by independent MP Andrew Wilkie, the other by Australian Marriage Equality - to the validity of the postal vote on September 5 and 6.

The parties challenging the validity of the postal survey argue the Turnbull government does not have the authority to appropriate the $122 million in funds for the vote.

They also claim the Australian Bureau of Statistics does not have the legal authority to conduct the survey.

"They are strong arguments [brought in the High Court challenge] ... Let's say 50-50," Mr Dreyfus told Insiders.

"The High Court is taking it seriously. There is an argument that says that there needs to be legislative authorisation before you can go out and spend $122 million of public money, and there isn't any legislative authorisation.

"And there's an argument that this is beyond power for the Australian Bureau of Statistics, under its legislation, to carry out this kind of very unusual activity.

"Let's hope for it to be more than 50 per cent [turnout] ... it's not going to have much worth if it's only 10 per cent or 15 per cent of people participating."

Mr Dreyfus also said Labor would examine laws the government has proposed that would subject the campaign to the usual electoral rules, including protections against malicious publications and bribery, which do not currently apply because the ABS is conducting the survey.

There are early indications that senior Turnbull government ministers, including the prime minister, plan to restrict their campaigning on same-sex marriage - either for a 'yes' or 'no' vote - to their own electorates, rather than using the national platform available to them.

Cabinet minister Josh Frydenberg appeared to confirm that approach on Sky News, saying he wanted a 'yes' vote and would be encouraging people in his electorate to vote that way.

"But when it comes to my broader position in terms of campaigning on this issue, I've got bigger fish to fry and that is energy policy and that will be my priority in the weeks and the months ahead," he said.

In contrast, Mr Dreyfus said: "I can understand why some people are simply disgusted, particularly in the LGBTI community, disgusted about this process that has been foisted on Australians ... If we must have this process, let's make sure it's a resounding 'yes'. I'll be voting 'yes', I will be campaigning for 'yes' and my colleagues are going to be campaigning for 'yes'".

City of Sydney City Liberal councillor Christine Forster, a vocal campaigner for a 'yes' vote and sister of former prime minister Tony Abbott, told Sky News that Australia's "culture of compulsory voting" would lead to a good turnout despite it being voluntary - but a close result would mean questions remained about legitimacy of the vote.

"There are sections of the Labor Party that are staunchly opposed to same-sex marriage. And it would open a real can of worms for the Labor Party if there was a resounding 'no' vote," she said.

"If there were, I think the Labor Party's position would be extraordinarily difficult in pursuing their commitment to pass legislation ... that is my worst nightmare."

Labor has, however, promised it will legalise same-sex marriage when it is next in office - regardless of the postal survey result.

The key dates for the plebiscite are September 12, when the ABS begins posting out ballots; November 7, when responses have to be received and November 15, when the result will be announced.

Australians have until August 24 to enrol or update their details with the Australian Electoral Commission.