The Australian Bureau of Statistics (ABS) has warned people not to post pictures online that show the unique barcode on their same-sex marriage survey forms, following a number of people doing exactly that after receiving the forms on Wednesday.
Australia Post will be sending out 600,000 survey forms per day in the coming weeks in order to reach the 16 million Australians on the electoral roll.
The unique barcode, which appears in the bottom right corner of the survey form, is used to link a specific form to an eligible voting Australian, in order to ensure no-one can respond to the survey more than once.
A spokesperson for the ABS told BuzzFeed News that mass fraud could not take place based on a barcode photo being posted online, but it could jeopardise a single response.
"A barcode won’t be counted more than once, that’s the whole point of the barcode," he said. "So if people were to reproduce it 100 times, that wouldn't be counted."
But it is a "plausible scenario" that someone could replicate a barcode based on a photo posted online and then submit a survey form on the behalf of the poster — as long as they did it before the original form had been returned.
"We would encourage people not to photograph their unique code and place it online," the spokesperson said.
The ABS marriage survey website says the barcode will be used to register the arrival of a form and is anonymous.
"No person who sees or has any access to any completed forms will know both the name of eligible Australians and the related single-use code," it reads.
The ABS also released updated information on what will invalidate a vote in the postal survey.
People should not cross out or rephrase parts of the question, as this will invalidate their survey response.
A tick, cross or shading in the relevant "no" or "yes" box will suffice for a valid answer. People should take care to not mark both boxes, or to scribble over the word "yes" or "no" marking the boxes in their response.
Anyone who loses their ballot or makes an error in filling it out can request a replacement from the ABS. The form must be returned by November 7.