Chocolate maker Mars announced it had secured "deforestation-free" supplies of palm oil.
The maker of M&Ms and Snickers said this week it had simplified and reduced the number of suppliers it buys from, ensuring the palm oil in its products does not harm forests.
It will slash the number of palm oil mills in its supply chain from 1,500 to less than 100 by 2021, it said, with the aim of halving it again in 2022.
Mars' chief procurement and sustainability officer Barry Parkin said the firm had worked to improve its palm oil supplies for more than a decade but three years ago realised buying only green-certified oil would not achieve the "completely sustainable palm" it wanted.
"Our conclusion - and that of many - is that certification is helpful but it does not guarantee deforestation-free," he told the Thomson Reuters Foundation.
The company now wants to move beyond making its own supply chain "clean" to challenging Mars suppliers to ensure their whole supply chains follow the same model, Parkin said.
If they do this, Mars will promise more business and longer contracts, he added.
Not all Mars' palm oil suppliers are yet deforestation-free throughout their entire operations, said Parkin, but they must be looking to achieve this within "a couple of years".
"It doesn't happen overnight," he said. "We're working with those that are committed to that journey. Anybody who says 'we'll get there in 10 years', we're not doing business with."
Mars' announcement could encourage others to follow, he noted, adding government regulation to force buyers to source sustainable palm oil would also help "get all actors in line".
Mars is a member of the Consumer Goods Forum that last month launched a new push to combat deforestation throughout supply chains and is working with smallholders, after many firms missed a 2020 "zero deforestation" target.
In 2019, tropical rainforests - whose preservation is considered crucial to limiting planetary heating - disappeared at a rate of one football pitch every six seconds, according to data from online monitoring service Global Forest Watch.
Environmentalists blame the production of palm oil - the most widely used edible oil found in everything from margarine to biscuits - for much of the destruction, as forests are cleared for plantations, mainly in Southeast Asia.
