Australians have 14 days to register to vote in the same-sex marriage postal vote.

Key points: People will have 14 days from Thursday to enrol to vote on same-sex marriage

People will have 14 days from Thursday to enrol to vote on same-sex marriage The ABS will run the process with ballots being distributed from next month

The ABS will run the process with ballots being distributed from next month Concerns raised over whether the outcome of a voluntary postal survey could be trusted

The ABC has learned the Australian Bureau of Statistics (ABS) will today announce Australians not already on the electoral roll will have until August 24 to register with the Australian Electoral Commission.

Acting Special Minister of State Mathias Cormann confirmed to the ABC's RN program that the Government wanted to provide as much time as possible for people to register and be given their say.

Senator Cormann defended the role of the ABS, saying the Government would be working with the ABS on rules to ensure the process is fair.

"This is now going to be a matter for the ABS to determine," Senator Cormann said.

In normal federal elections run by the Australian Electoral Commission registration closes seven days after writs.

For the postal vote, people have 14 days from today to enrol to vote, if they have not already, or update their details if they have changed since the last election.

The ABS will run the process with ballot papers going to every enrolled Australian from next month, to be returned by November 7 and a result on November 25.

There will be a chance for Parliament to vote later this year, but there is no guarantee that will happen and MPs will not be bound by the result of the postal survey.

Independent MP Andrew Wilkie and other same-sex marriage advocates have already launched a court challenge against the voluntary postal survey.

While Labor Senator Penny Wong told the Senate that children would be "exposed to hatred" by the push for a public vote.

Sorry, this video has expired Penny Wong delivered an emotional speech after Australian Christian Lobby's 'stolen generation' remark.

Concerns raised over ABS' role

The union representing ABS employees, the Community and Public Sector Union (CPSU), has serious concerns about the capacity of the department to run the postal vote.

CPSU deputy secretary Melissa Donnelly said the agency was "already under massive pressure and struggling with its core functions after two rounds of job cuts".

"As has been shown in recent times by 'Census fail' and also some issues with employment and other economic data," she said.

"The CPSU has been contacted by a number of ABS staff who are deeply worried about this decision.

"The Government's argument that this situation is nothing new because of the national anthem poll run by the ABS in 1974 is ridiculous — In that case 60,000 people were surveyed over the telephone as part of the ABS's regular statistical work.

"A postal plebiscite is a completely different process."

Constitutional law experts raised fears about whether the outcome of a voluntary postal survey could be trusted.

Professor George Williams said there were experts in our country whose job it was to conduct sensitive national votes, but those experts were not the Australian Bureau of Statistics (ABS).

"It's a body that fulfils a different set of functions," he told the ABC.

"I was mystified by it. I'm still finding it hard to understand why such a sensitive, contested process wouldn't be left to the experts within government — that's what the AEC [Australian Electoral Commission] does."

The debacle with the ABS-run census has Professor Williams worried. He said "this could go very wrong" if the ABS has to cobble together a roll-out in a short space of time.