Chris McManus, the sponsor of Initiative 522, arrives at the secretary of state's elections division office to drop off petition signatures, in Olympia, Wash. The measure would require the labeling of any food and seeds sold in Washington that were produced through genetic engineering. Image: Rachel La Corte, APCompanies would be required to label food products made from genetically engineered crops under a Washington state initiative submitted by the proposal's sponsors.

Sponsors of the initiative delivered 350,000 signatures to the Secretary of State's office inside an ambulance with a sign reading "Label GMO Food" on the side.

Initiative 522 would require food and seeds produced entirely or partly through genetic engineering and sold in Washington to be labeled as such, effective July 1, 2015. Under the measure, raw foods that are not packaged separately would have to be labeled on the retail shelf.

The proposal comes two months after California voters rejected a similar ballot measure in a nearly $55 million advertising war that pitted food safety advocates against agricultural and biotechnology giants. Supporters argued consumers should have a choice of whether or not to eat genetically engineered products, even though the government and major science groups say such foods are safe to eat. Opponents argued the proposal would raise food prices and hurt farmers.

About 50 countries require genetically modified foods to be labeled, but the U.S. isn't one of them. Only Alaska has enacted legislation at the state level, requiring the labeling of genetically engineered fish and shellfish products.

A bill in the Washington Legislature to require food labeling failed to pass out of committee, despite support from a coalition of local wheat farmers who says they feared their export markets will be hurt if genetically modified wheat gains federal approval.

Biotechnology giant Monsanto Co. has announced plans to begin testing genetically modified wheat, though the product is likely a decade or more from being offered commercially.

An initiative to the Legislature requires at least 241,153 valid signatures of registered state voters to be certified, though the secretary of state's office suggests at least 320,000 as a buffer for any duplicate or invalid signatures.