Auckland Zoo has dropped Cadbury products from its shelves because the confectionery manufacturer has begun using palm oil in its chocolate.
The zoo says palm oil production is the leading cause behind the destruction of rainforests in South East Asia, the main habitat of species such as orangutans.
Cadbury says on its website that palm oil is now used in its products but says it is a member of the Roundtable for Sustainable Palm Oil.
Auckland Zoo's primate team leader Amy Dixon says rainforest is being cleared and burned at a fast rate to make way for palm oil plantations.
The product is used in a wide range of products, from processed food to cosmetics, she says, and the zoo is committed to reducing the amount of palm oil it uses, including in its animal feed.
Ms Dixon says New Zealand does not require palm oil to be specified on labels so the zoo is writing to manufacturers to find out whether the vegetable oil they are using in their products is palm oil.
She says a company's membership of the Roundtable for Sustainable Palm Oil does not constitute proof that it is sourcing palm oil sustainably.