The chairperson of the Safer Future Charitable Trust says he has no idea how Vote Safe flyers could've ended up in EasyVote envelopes distributed by the Electoral Commission.
The envelope contains an EasyVote card, candidates for the electorate the recipient is in, contact details from the returning officer, and official information on the referendums.
But the commission has confirmed it has received more than one complaint that a pack also contained publicity material from the Safer Future Charitable Trust.
The trust is behind the Vote Safe campaign - a group that opposes the End of Life Choice Act.
"We've obviously put out our flyer in letterboxes and we've had a few notifications that these flyers have somehow ended up in these sealed EasyVote envelopes which is just bizarre," Trust chairperson and VoteSafe campaign manager Henoch Kloosterboer told Morning Report.
VoteSafe's flyers were printed in the same facility as the flyers for the Electoral Commission, Kloosterboer said.
"There is a chance of human error there, potentially."
Kloosterboer said he believed it would be a 'low number' of his campaign's flyers that ended up in the EasyVote packs, but encouraged anyone who found them in their packs to get in touch with his Trust and the Electoral Commission.