An agri-chemical industry body is calling for Trade Me to ban the sales of pesticides if they have been opened or are being sold in used bottles.
Agcarm chief executive Mark Ross said it had been pushing for a ban on selling these products on Trade Me but the practice was continuing.
It is illegal to sell pesticides once they have been opened, under the Hazardous Substances and Organisms Act.
Agcarm chief executive Mark Ross said there was a good reason for regulations on how chemicals must be packaged, labelled, transported and used for a good reason, and that was people's safety.
The association's members had spotted illegal auctions on Trade Me on a regular basis.
"For example, weed killers being sold in plastic Fanta bottles, products being sold in containers that have been opened, so the lid is loose and then they're transported illegally in the back of cars and could easily spill," Mr Ross said.
"It's just a risk that they could be drunk accidentally by a child... it's just ensuring that they're sold in the right place, by the right people."
Agcarm was meeting Trade Me next week about its concerns, he said.
"It was sort of raised last year and it's been on going for a number of years but it really hit the head last year when we came across products in plastic Coke bottles and Fanta bottles being sold."
Trade Me head of trust and safety John Duffy said the site did not allow the sale of pesticides in open bottles and the listings would be removed if they were detected.
Trade Me had adequate screening systems to stop these kind of sales, he said.
"I think this issue has kind of been blown a little bit out of proportion ... Agcarm represents the industry and there's an interest there in people not re-selling chemicals, they want people to be buying new chemicals.
"Our discussions with the Environmental Protection Authority is that they don't necessarily see it as a major problem and it's not really on their radar either."