DENVER (AP) – A proposal requiring genetically modified food to be labeled is headed to Colorado’s ballot.

Backers of the proposal have collected enough valid signatures to place it on November’s ballot as Proposition 105, Secretary of State Scott Gessler said Wednesday. The Right to Know Colorado campaign turned in a petition with 171,387 signatures, nearly twice as much as required. Based on a random sample, Gessler’s office estimated that 124,905 were valid.

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Earlier this year, Colorado lawmakers rejected a proposal asking food producers to voluntarily label food made with genetically modified crops, known as GMOs.

Many countries require GMO food to be labeled, but the United States does not have such a rule. Three states – Vermont, Connecticut and Maine – require such labels.

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Voters in Oregon will also get to decide this fall whether to require GMO labels.

There is little science that says genetically engineered foods are unsafe. Opponents say little is known about them, so consumers have a right to know if they are eating them.

The Colorado proposal would require producers to start using the labels by July 1, 2016. Food produced from animals that haven’t been genetically engineered themselves but have eaten genetically modified food would be exempt.

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