The Australian Bureau of Statistics says some marriage survey ballots have been returned with razors blades inside the envelopes.
Despite warnings early in the survey period that this would invalidate votes, ballots have also been posted with dirt or glitter in the envelopes, according to Pink News.
The marriage equality survey closes next Tuesday 7 November, with the Australian Bureau of Statistics having advised voters to mail their ballots by last week to ensure they are received and counted.
The latest figures show more than 70 per cent of votes have been received.
Lyle Shelton, the face of the No campaign, last week called marriage equality “snobbery”.
“There’s only about 20 or so [countries] out of 200 that have redefined marriage,” he said at an event in Coffs Harbour.
“It’s only a few western countries that have decided they’re better than the millennia of human history and anthropology, so they redefined marriage.
“I think we’re showing a lot of chronological snobbery in a handful of countries in the west.”
Shelton argued that despite Australia not having marriage equality, gay people are treated equally.
“We want to preserve the definition of marriage between a man and a woman,” he said.
“Our gay friends already have equality under the law, there is no discrimination in the Australian law against gay couples.”
The results of the marriage equality survey will be announced on November 15.