Chefs Back Measure on Labeling G.M.O.'s More than 700 of the nation's chefs and professional foodies, from prominent names like David Bouley to up-and-comers like the chef Bryant Terry of Oakland, have lined up to support a California ballot measure that would require food companies to label products containing genetically engineered ingredients. "We're talking about the provenance of food, and there's nothing more important to chefs like me," said Alice Waters, the founder of Chez Panisse in Berkeley, Calif., and legendary proponent of locally grown foods. We need to know where our food comes from and how it's produced, who produces it. That's the bedrock of what we do. Ms. Waters said she initially thought she needed to do no more than vote "yes" for the ballot measure, Proposition 37, when she went to her polling place on Nov. 6. But a visit to Sonoma County from Carlo Petrini, the founder of the slow food movement, convinced her that she needed to become more active. "He had come to talk about Slow Food and the change in leadership, but the first thing he started talking about was Prop 37," Ms. Waters said, referring to the nonprofit Mr. Petrini founded in 1989 to nurture the movement. He talked about Europe looking to the vote in California and how we needed to take this on, and I decided then that I needed to do whatever I could. I needed to get active. So she sent out an e-mail late Friday night, asking chefs she knew around the country to lend their support to the campaign to get the ballot measure passed. By Monday morning, 100 chefs had signed up, and 200 more quickly signed on once word got out on Twitter and other social networks. On Tuesday, Mr. Bouley became the 516th chef to sign onto the cause. "Whether it's calorie labeling in chain restaurants or chefs putting on their menus what farm they bought the lamb from, people want to know more about their food and where it comes from," said Peter Hoffman, chef and founder of the now-closed Savoy, a farm-to-table pioneer in SoHo, and the Back 40 restaurants. So this isn't about whether G.M.O. is right or wrong, it's about transparency. And when someone opposes transparency, what does it tell you? Mr. Hoffman noted that avoiding foods with genetically engineered ingredients is becoming harder and harder. For instance, he said he recently learned that most white vinegar sold in supermarkets comes from corn and thus is likely to be genetically modified. Dan Barber, the executive chef and an owner of the Blue Hill restaurants, joked that he himself engages in genetic engineering at Blue Hill Farm in Great Barrington, Mass., which supplies some of the ingredients used in the dishes he makes at his restaurants. The current menu, for instance, features a new, proprietary variety of squash he and his crew at the farm have grown by cross-breeding conventional squashes. "That sometimes results in some outrage from customers initially until we explain what we're doing," Mr. Barber said. But he makes a distinction between what he is doing and what the food and agribusiness companies that have poured tens of millions of dollars into opposing the ballot measure are doing. "They are inserting genes at will, sometimes from completely different species, and creating things in a lab that would never occur in nature," Mr. Barber said. We don't support that.