The society is pushing for precise labelling of ingredients to be set in legislation on products in the market.
Manufacturers are able to use the terms vegan and vegetarian without any standards applying, and some of those products may still contain animal ingredients, Vegan Society spokesperson Claire Insley told RNZ's Afternoons programme today.
A product may have a sticker saying, plant based or less dairy, she said.
"They might think that's okay I can eat that, and they take it home and it's only then when they search through the ingredient list that they find out in fact there is milk powder in it, or gelatine or even meat."
There are no specific rules governing the use of the words vegan, vegetarian and plant-based, she said.
"Unfortunately, the Food Standards Authority doesn't have these terms defined, so people can write these things and it may not mean what the rest of us would believe it to mean.
"Plant based is quite a buzzword nowadays and some manufacturers are keen to write plant based on their products, even if they are not 100 percent plant-based and unfortunately most of the people actively looking for plant-based products are in fact looking for 100 percent plant-based products."
Some products which say vegan friendly simply mean the factory also processes non-vegan products, she said.
"The product itself is fully vegan, the ingredients are all vegan, but the reason they say it's vegan friendly is because it is produced in a factory that may produce non-vegan products, so there is the chance of cross contamination."
The society is launching a petition to change the legislation, she said, following approaches to the Ministry for Primary Industries (MPI) and the Commerce Commission.
"Because it is so messy, because we do have things like plant based being used on products that are not 100 percent plant based and even some products you can buy in New Zealand that say vegan but may contain honey, so it isn't actually vegan."
Some labelling is "bizarre", she said.
"There's no point writing less dairy on a product. What does that mean? Less dairy than what? It doesn't make sense.
"We want to avoid confusion and just stick with what actually is in the product and not have these random, bizarre, misleading and uninformative labels."
