Two decades after genetically modified foods first hit the shelves of American supermarkets, a fight is sprouting over whether consumers should be told more about what's in their grocery bags. Even though most processed foods now contain at least one genetically modified ingredient, there's no national requirement in the United States for manufacturers to disclose GM content, unlike in the European Union and many countries elsewhere. Despite years of widespread use across the US and repeated safety approvals, campaigners still think that genetically modified organisms, or GMOs, are risky or unhealthy. They're working in many states across the country for tougher regional labelling laws. "I don't think there is anything wrong with how nature designed our food and I don't think we know enough about the long-term effects," said Kathryn Lowe, a Portland-based massage therapist and health coach. Lowe told AFP she was helping to gather signatures to make sure a law is presented to Oregon voters on the November ballot. It would require food makers to clearly put "produced with genetic engineering" on GMO-containing products. Many states allow residents to vote for new laws, and campaigners in Colorado are aiming for a similar measure. They say GMOs were released onto the mass market without enough independent testing of their long-term safety. The debate goes to the heart of America's multi-billion-dollar agriculture and food-technology industries. Not surprisingly, these groups are fighting to eradicate the spread of such requirements and say campaigners' arguments are unfounded - or just plain wrong. "Mandatory labelling could imply that food products containing these ingredients are somehow inferior to their conventional or organic counterparts," said Charla Lord, a spokeswoman for Monsanto, one of the biggest players in the biotech field. "To say that GMO crops are 'untested' or 'unsafe' is simply not true. GMO crops undergo more testing and oversight than any other agricultural products and the safety of biotech crops is well-established," she added in an email. Monsanto produces many genetically engineered crops, including a line of corn and other plants that have been altered to tolerate higher doses of the company's own popular herbicide, called Roundup. Almost all corn, soy, sugar beet and canola crops in the US are genetically engineered. Organic foods are by definition GMO-free. The EU has mandatory labelling for GMOs or products with genetically modified ingredients. Supporters of labelling laws say consumers should be told in greater detail about what they're actually eating. They point to recent polls, including by the New York Times and Consumer Reports, that suggest nine out of 10 Americans support this. "This is a no-brainer. There should be a national law requiring GMO labelling and there should be independent testing," said David Rosenfeld, the executive director of an Oregon consumer group called OSPIRG. He said genetically engineered crops had been linked to a more than 400-million-pound (181-million-kilo) increase in pesticide use in the US between 1996 and 2011, and that this carried risks to health and the environment. Campaigners in Oregon and Colorado are hoping to learn from similar recent initiatives that failed, notably in California in 2012 and in Washington state last year. Agro-chemical and agro-food giants such as Monsanto, Bayer, DuPont, Coca-Cola, and PepsiCo, poured millions into defeating the ballot initiatives, vastly outspending backers. Labelling proponents say they've tweaked the wording of their proposed laws to protect them from food-industry attacks. And this year, the north-eastern state of Vermont took the historic step of passing a mandatory labelling law. Maine and Connecticut have also approved labelling measures, though these won't take effect unless several contiguous states first adopt similar requirements. The Grocery Manufacturers Association, along with other food groups representing mainstream US food producers, has sued Vermont over its labelling law. "Mandatory GMO labelling at the state and local level would only be confusing and costly for consumers and those who grow their food," said GMA spokesman Brian Kennedy in an email. "These differing standards would require food producers to establish different supply chains for different states, creating enormous expenses that could be passed onto consumers," he added. Campaigners say such claims mislead consumers and amount to scaremongering. "Those are all nonsense figures," said Michael Hansen, a senior scientist at the Consumers Union. He said the actual difference would really be just a few cents. In many towns, signs abound that people want to know what's in their food and companies are capitalising on this. Supermarket chain Trader Joe's says its products are GMO-free. Here in Portland, a hip and alternative city in the Pacific Northwest, restaurants and food trucks cater to just about every possible diet, and menus often state that foods are GMO-free where possible. In rural southern Oregon, two counties in May voted to ban the growing of genetically engineered crops over fears that genetically modified seeds could contaminate organic and non-GMO crops.