They claim the Fairtrade mark's reputation risks damage because of its association with the food giant.
Baby Milk Action has added the Nestle Fairtrade Partners' Blend brand to its list of boycotted products after the coffee was awarded a Fairtrade mark last Friday.
The Fairtrade Foundation's decision has created division among campaigners and charities over whether Nestle is genuinely trying to be a better corporate citizen or whether it is jumping on the Fairtrade bandwagon as a marketing ploy.
Baby Milk Action, which co-ordinates the international Nestle boycott, has been the most vocal in condemning the decision, principally because of what it describes as the company's "aggressive marketing of baby foods".
Mike Brady, its campaigns co-ordinator, said: "For many, support for the Nestle boycott and promoting fair trade go hand in hand, so the decision by the Fairtrade Foundation to award Nestle with a mark creates a dilemma.
"Campaigners have already warned of possible damage to the Fairtrade mark by its association with the UK's most boycotted company."
Brady also expressed disappointment that the foundation had not consulted more widely among members before awarding the mark, despite this concern being voiced in regular talks between Baby Milk Action and the Fairtrade Foundation.
However, a spokeswoman from the Fairtrade Foundation said that Baby Milk Action was not a member and so would not have been formally consulted; but it had been kept fully informed of progress and told of the launch.
"Members of the foundation's board were kept fully informed throughout, and they are part of the decision-making process," she said.
She also said the foundation's motive for granting the mark to Nestle was to get all coffee roasters to improve their practices in developing countries rather than start an argument among NGOs.
Harriet Lamb, director of the foundation, said: "With this product, Nestle is recognising the value of the unique Fairtrade system with standards including the guaranteed minimum price for marginalised, small-scale coffee farmers and the importance of independent verification of these standards so that consumers know what they are buying."
A spokesman from Christian Aid, one of the Fairtrade Foundation's board members, declined to say whether it had been consulted. He said: "Christian Aid notes that our sister organisation the Fairtrade Foundation has endorsed one of Nestle's products. This does not mean endorsement of Nestle as a company, just Fairtrade's certification of one of its products.
"We challenge Nestle to make sure all of its products are fairly traded, and we will monitor Nestle to ensure it does not use this merely as a publicity stunt to earn kudos."
- The Fairtrade Foundation has awarded a mark to Nestle's Partners' Blend coffee brand
- Baby Milk Action has added the brand to its list of boycotted products
- Campaigners have warned that the mark's reputation could be damaged because of its association with Nestle
- The Fairtrade Foundation said members of its board were part of the decision-making process
- The foundation said its motive for granting the mark was to encourage all coffee roasters to improve their practices in developing countries.