An effort to label genetically modified foods in Colorado failed to garner enough support Tuesday. It's the latest of several state-based GMO labeling ballot measures to fail. UPDATE:A similar measure in Oregon was also defeated by a narrow margin.

Voters in Colorado resoundingly rejected the labeling of foods that contain the derivatives of genetically modified - or GMO – crops, with 66 percent voting against, versus 34 percent in favor.

In Oregon the outcome was closer, with fewer than 51 percent voting against the measure. Political ad spending in Oregon was more competitive than in Colorado, where labeling opponents outspent proponents by millions of dollars.

Meanwhile, a proposal in Maui County, Hawaii, skipped the labeling debate altogether. Voters there narrowly approved a moratorium on GMO crop cultivation. The state has been a battleground between biotech firms and food activists. Some Hawaiian farmers grow a variety of papaya genetically engineered to resist a plant virus.

Polling prior to the GMO labeling vote in Colorado was scarce. Polls found Colorado's measure faced an uphill battle in the final weeks before the election. A Suffolk University poll found only 29 percent of registered voters favored the measure, while 49 percent were likely to vote against it. A Denver Post poll was even more damning. According to that poll, 59 percent were opposed to GMO labeling in Colorado, 34 percent in favor.

Colorado's Proposition 105 would've required food companies to label packaged foods with the text "produced with genetic engineering." Oregon's Measure 92 says food labels would need to include the words "genetically engineered." Many processed foods contain soybean oil, corn syrup, refined sugar and cottonseed oil. Those oils and syrups are often derived from GMO crops that farmers have adopted over the last 18 years. Few whole foods, like the ones you see in the produce aisle, are genetically engineered, though some GE varieties of sweet corn, squash and papaya are approved for sale in the U.S.

The failed measures in Colorado and Oregon follow a nationwide trend. Similar ballot questions in California and Washington state were rejected in 2012 and 2013, respectively. This summer, Vermont's governor signed the nation's first GMO labeling requirement into law. It's supposed to take effect in 2016, but a coalition of biotech firms and farmer groups have filed suit to prevent that from happening.

Groups opposed to GMO labeling poured big money into efforts to quash the ballot measures, spending more than $15 million in Colorado alone. In Oregon, opponents of labeling raised more than $18 million, making the ballot measure the most expensive issue campaign in the state's history. Most of that money came from large seed corporations like Monsanto and DuPont Pioneer, and from processed food companies like Pepsi, Land O' Lakes and Smucker's. All of that outside money opened labeling opponents up to criticism of being tied to corporate interests.

"The reality is, campaigns cost money, and I'm really proud to say that groups like Smucker's, like Pepsi, stood shoulder to shoulder with the farmers that are growing their ingredients," says Chad Vorthmann, executive vice president of the Colorado Farm Bureau, which also contributed to the "No on 105" campaign.

Supporters of GMO labeling efforts took issue with opponents' claims that the measure would result in the cost of food going up and increase the burden on farmers. Despite Tuesday's loss at the ballot box, Andrew Kimbrell, executive director of the national , which supports labeling efforts, saw a silver lining in the outcome.

"Despite an aggressive and deceptive anti-consumer campaign, hundreds of thousands of Colorado voters spoke up in favor of GE food labeling," Kimbrell said in a statement.

Even with a down vote in Colorado, don't expect a dramatic shift in the debate around genetically modified crops.

Labeling proponents say the elections have been bought, not just in Colorado but in California and Washington state as well, and vow to keep trying. Earlier this year, the Grocery Manufacturers Association – which includes members like Kraft and Pepsi — proposed its own voluntary national labeling standard, but that effort has yet to gain any significant traction at the federal level.

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