A number of same-sex marriage postal survey forms have reportedly cropped up on online auctioning sites.

One seller reportedly offered their postal vote form for a starting bid of $1500 on eBay, according to ABC News .

The Australian Bureau of Statistics (ABS) has now reportedly referred up to 20 similar cases to the Australian Federal Police.

ABS deputy statistician Jonathan Palmer told ABC News he is working closely with eBay and Gumtree to stop people from selling their forms.

“We are constantly monitoring those market places…asking them to take stuff down,” Mr Palmer told the broadcaster.

Buying or selling submitted survey forms is considered a criminal offence under the Census and Statistics Act.

It comes amid reports some people are stealing the ballot forms, which are filled out anonymously, from letter boxes.