BALLARD, an up-and-coming neighbourhood in north-west Seattle, was once populated by hard-drinking Norwegian fishermen. Today it is home to a more refined set. “I love pea hummus,” purrs a diner at the Golden Beetle, a local organic restaurant, as a streetcar glides pleasantly past outside. Other customers dig into herbed falafel and (delectable) black-walnut baklava.

Seattle’s diners are a savvy lot, says Maria Hines, the restaurant’s owner. That may be why Washington state has become the latest target for partisans in America’s food-labelling war. Initiative 522, a measure currently before voters (and strongly backed by Ms Hines), would require most foodstuffs sold in retail outlets to bear a conspicuous label if they contain genetically modified (GM) ingredients. The rule would come into force in July 2015 for any product where GM ingredients are more than 0.9% of the total weight; by July 2019 the threshold would drop to zero—an impossible standard, say critics. Voting closes on November 5th.

At least 70% of the processed foods in American supermarkets contain GM ingredients. The technology boosts yields, reduces pesticide use and is a crucial tool in the struggle against global hunger. Americans have been munching GM food for two decades without ill effect, and nearly all scientists believe that GM crops are safe. But many greens and organic-food enthusiasts disagree. The EU made labels compulsory in 1997; consumers were spooked and GM food is now rare in Europe.

Transparency for consumers is an attractive rallying-cry. Generic polling finds over 90% of Americans in favour of GM labelling. Before the I-522 campaign began, a large majority of Washingtonians said they backed the measure. But a well-run opposition campaign focused on the exemptions and costs of the proposal has cut the lead from 45 to four percentage points in six weeks. Stuart Elway, whose polling firm uncovered these numbers, says that in four decades of observing state politics he has never seen opinion move so quickly.

No state has passed a GM-labelling measure at the ballot. Last year in California Proposition 37, on which I-522 was based, foundered after squandering a huge polling lead. Repeated attempts to pass federal labelling laws have gone nowhere. Yet change may be afoot. In June the legislatures in Maine and Connecticut passed GM-labelling laws (although they will not come into force until other states follow suit). Labelling bills were introduced in 24 other states this year, says Just Label It, a pressure group. Several retailers and manufacturers have made GM-free pledges this year. And at a meeting in January food makers and retailers, bruised by the California battle, were reported to have backed the idea of a federal labelling rule which they could help draw up.

That push appears to have gone quiet as the I-522 campaign has heated up. But “people’s heads will spin” at the speed of its revival if the measure passes, says Charles Benbrook, an agriculture professor at Washington State University. Other states will quickly pass similar laws, he predicts. Rather than deal with endless campaigns and a patchwork of rules, supermarkets, manufacturers and even biotech firms will lobby for a federal law. In September Ken Powell, the boss of General Mills, a big food producer that contributed to the “no” campaigns in both California and Washington, told investors that he backed a federal labelling rule.

The campaign in Washington is the second-most-expensive in state history. I-522’s proponents (biggest single backer: Dr Bronner’s Magic Soaps) portray themselves as David squaring up to Goliath. Their opponents (biggest backer: Monsanto) have indeed raised almost three times as much money, and from a narrower, richer range of donors; the median contribution to the “yes” campaign is just $25. But its ads are just as slick, and its message—for consumer information rather than against GM techniques—equally refined.

The rhetoric is heated. I-522’s opponents accuse the other side of peddling baseless scare stories. One fan of the measure compares the struggle to the emancipation of slaves. For Mr Benbrook, the concern is that a drawn-out battle over labelling will distract from more important things, such as identifying the most beneficial applications of GM technology in food production, or ensuring that the federal government adopts a more independent approach to testing.