By Suzanne Goldenberg, Guardian UK

Industry giants are spending more than $25m to defeat campaigns for mandatory GM food labelling in the two states, in the runup to next month’s vote

Biotech and supermarket giants are spending more than $25m (£15.6m) to defeat ballot initiatives in two western states that would require labelling of foods containing genetically modified organisms.

In Colorado, Dupont and Monsanto food companies are outspending supporters of mandatory labelling by 22-1 ahead of the 4 November vote, according to state campaign finance records.

In Oregon, meanwhile, industry is outspending supporters of the ballot measure by about 2-1.

The heavy industry spending resembles the last-minute infusions of cash for television ads, direct mail, and campaign staff that helped defeat earlier campaigns for mandatory GM labelling in California and Washington state.

“It is like David vs Goliath,” Larry Cooper, director of Colorado’s Right to Know campaign said.

He said the pro-labelling campaign had raised $625,000 by Thursday afternoon. Cooper’s opponents, meanwhile, amassed $14m, after Dupont this week gave an additional $3m to the campaign, and were advertising heavily on local television.

“Why they put $14m in Colorado to keep us in the dark really doesn’t make sense to me,” Cooper said. “The bottom line is that we really don’t know what is in our food. We are shopping blindly.”

Monsanto alone has spent $4.7m to defeat the measure. Other top donors to the campaign to defeat pro-labelling Proposition 105 read like a grocery shopping list. They include: Pepsico, Kraft Foods, General Mills, Hershey Company, Coca-Cola and Kellogg, and Flower Food, according to Colorado state campaign finance records.

The spending is much less lopsided in Oregon where opponents of the state’s Measure 92 labelling initiative have raised $11m while supporters have $6m.

Monsanto is a major force in both states. “We oppose state-by-state mandatory labelling laws like Measure 92 in Oregon and Proposition 105 in Colorado,” a company spokeswoman said in an email. “The reason we don’t support them is simple. They don’t provide any safety or nutrition information and these measures will hurt, not help, consumers, taxpayers and businesses.”

Unlike Colorado, labelling advocates in Oregon have attracted some big donors to their side, including $1m from Dr Bronners’ magic soaps.

An heir to the Hormel meat-packing fortune. Thomas Hormel, who has no connection to the company and lives in Florida, gave $500,000, according to state campaign finance records.

The company immediately ramped up its own donations, giving a total of $85,000 to defeat the labelling initiative.

Kevin Glenn, a spokesman for Oregon Right to Know, said the pro-labelling side hoped to counter the financial advantage by grassroots organising. He said the campaign had opened five field offices in the state, and was about to start canvassing door-to-door.

Organisers also had a bit of a head start. In May, voters in two rural counties voted to ban cultivation of GM crops, on the grounds that it put conventional produce at risk of contamination.

Last year, a number of countries postponed wheat imports from Oregon after an outbreak of GM wheat from an experimental research station. Investigators have yet to discover the source of the GM outbreak, which occurred years after the tests were shut down.

Scientists generally agree that foods containing GM ingredients are safe to eat, but the “right to know” has emerged as a hugely emotional issue for some Americans.

Pro-labelling campaigners say the public has a right to know exactly what they are eating. Opponents say labels make no sense if there are no real health concerns, and risks stigmatising their products.

Vermont earlier this year became the first US state to adopt mandatory labelling of GM foods – although the law does not go into effect until 2016.

Maine and Connecticut have also passed GM labelling laws, but put them on hold.