Voters in Colorado rejected a measure to require labeling of foods made with genetically modified ingredients, and a similar Oregon initiative looked headed for defeat on Tuesday.

The outcome at the polls came after corporate food and agriculture interests poured more than $36 million into anti-labeling campaigns in the two states.

The same group of companies, which include the biotech seed and chemical companies Monsanto and DuPont, helped defeat similar measures in California and Washington state in 2012 and 2013.

The Colorado labeling measure captured only about 32 percent voter approval, versus 68 percent opposed, according to preliminary results. Opponents raised more than $16 million on efforts to kill the measure, compared with $895,000 raised by those pushing for passage, according to the secretary of state's office and campaign finance filings.

In Oregon, where labeling opponents put together more than $20 million for campaigning, compared with $8 million raised by supporters, the initiative was failing by 51.4 percent to 48.6 percent, according to preliminary results.

Several other states are eying GMO labeling measures. Labeling proponents say GMOs can be harmful for humans and the environment. But opponents say GMOs have been proven safe and that mandatory labeling would be costly and confusing for consumers.

Connecticut and Maine have passed GMO labeling laws, but both states require other states to pass labeling bills before the laws take effect. Vermont has passed a mandatory labeling law with no other requirements. It is set to take effect in 2016, but labeling opponents have sued to try to block the law.