Mars said that, starting with the Galaxy chocolate bar favored in Britain and Ireland, it would include a seal of approval from a New York non-profit group called Rainforest Alliance, The Washington Post reported Friday.
The seal indicates the cocoa comes from farmers who meet certain labor and environmental standards.
Mars said the move would ensure its supply line, but Marcia Mogelonsky, a senior analyst at marketing firm Mintel it would also appeal to socially conscious consumers. A month ago, Cadbury said it would align itself with the Fairtrade Foundation's standards for some of its products.
Mars said it would not raise the price of its products, although the move is likely to cost tens of millions of dollars.
"The chocolate industry, like the coffee sector, is quickly waking up to the fact that they need to address their supply chain all the way back to the farmers," said Chris Wille, head of the Rainforest Alliance.
"If not," he said, "they may not have all the raw ingredients ... they need."