Whole Foods Market, the grocery chain, on [March 8] became the first retailer in the United States to require labeling [by 2018] of all genetically modified foods sold in its stores, a move that some experts said could radically alter the food industry. The announcement ricocheted around the food industry and excited proponents of labeling. Fantastic," said Mark Kastel, co-director of the Cornucopia Institute, an organic advocacy group that favors labeling. The Grocery Manufacturers Association, the trade group that represents major food companies and retailers, issued a statement opposing the move. The labeling requirements announced by Whole Foods will include its 339 stores in the United States and Canada. Since labeling is already required in the European Union, products in its seven stores in Britain are already marked if they contain genetically modified ingredients. The labels currently used show that a product has been verified as free of genetically engineered ingredients by the Non GMO Project, a nonprofit certification organization. Gary Hirshberg, chairman of Just Label It, a campaign for a federal requirement to label foods containing genetically modified ingredients, called the Whole Foods decision a "game changer." He compared the potential impact of the Whole Foods announcement to Wal-Mart's decision several years ago to stop selling milk from cows treated with growth hormone. Today, only a small number of milk cows are injected with the hormone.