The world's biggest food and chemical companies are closely watching Washington state for a potentially industry-changing vote on Nov. 5, when residents will either approve or reject a law that would require manufacturers to "clearly and conspicuously" display labels on foods made with genetically modified ingredients starting in 2015.

If the measure, Initiative 522, passes, Washington would be the first state in the U.S. to require GMO labeling, signaling a huge shift for the packaged food industry. The vast majority of the country's corn and soy crops — used to make crackers, cookies, juice, cereal, and tons of other packaged foods — are grown with genetically modified seeds.

There are currently similar legislative proposals in 22 other states, but all eyes are on Washington. "[The vote in Washington] will be kind of one for you to watch and see which way the wind is blowing with respect to customers saying 'this matters to us,'" said Whole Foods CEO Walter Robb on a call with analysts earlier this month. Starting in March 2018, Whole Foods will require all products in their stores to be labeled if they contain GMOs.

Those against the labeling bill point to the many studies showing GMO foods to be safe for human consumption, but labeling proponents are more concerned with transparency. A recent poll conducted by the New York Times showed that this is information consumers want to have: 93% of the American public thinks foods containing GMO ingredients should be identified.

Food companies including Coca-Cola, Pepsi, Campbell Soup, and Hershey already sell GMO-labeled products in some of the 60-plus other countries around that world that require it, but have fought hard to avoid putting the same information on drinks and snacks in the U.S., their biggest and most lucrative market. So far, it's worked: Deep pockets and effective lobbying through the GMA, the Grocery Manufacturers Association, have helped stall or defeat both state-by-state legislation and a nationwide FDA ruling to require labeling.