France, Sept. 21 -- The French supermarket giant Casino has been threatened with legal action by a coalition of NGOs who accuse it of selling beef linked to illegal deforestation in the Amazon.

French, American and Colombian NGOs on Monday warned Casino that it has three months to comply with duty of vigilancelaws regarding its supply chains in South America, where it is a leading supermarket retailer.

Lawyers for the coalition delivered the ultimatum in a letter of formal notice that was sent to Jean-Charles Naouri, the CEO of the Casino Guichard-Perrachon group.

The move follows a field investigation in June by the French NGO Envol Vert, which found that Casino's suppliers "regularly purchased" beef from four farms involved in defore...