The battle for California voters has begun.

California's government leans heavily on a system of referendums, with voters tasked with approving or denying measures like the rate of property tax, gay marriage and the high-speed rail system. On November, Proposition 37 will be on the ballot. The proposition hopes to put labels on foods that have been genetically modified.

Unsurprisingly, the battle has gotten very expensive, very quickly. Agribusinesses and food manufacturers have donated a total of $13 million toward defeating the measure, bringing the total up to $25 million in the coffers of those opposing the proposition. In comparison, the organic farmers and environmentalists who support the proposition have managed to raise less than a tenth of that total amount.

Similar measures have been proposed and defeated in other states, but a victory in California could turn the tides. The proposal could affect tens of thousands of name-brand products, which is why companies like Coca-Cola, DuPont and Nestlé have all pitched into the effort of defeating the proposition.

Proponents of the label system say that consumers deserve to know what is in their food, mentioning food-safety concerns and a general distrust of connections between agriculture and corporate interests.

But opponents' concerns are multifold. Some have grumbled that the measure is "anti-science," as Bob Goldberg, a plant geneticist at UCLA put it. Some add that the labels could be thought of as warnings, stoking public sentiment against genetics. Others argue that the label would increase food costs, and expose grocers and distributors to unnecessary lawsuits because of incorrect labels.

The consequences of labeling would be widespread as well. As much as 94 percent of soybeans and 88 percent of corn grown in the United States has been genetically modified to resist herbicides, pesticides or both. The labels would also not reflect how the foods have been modified or how much modification occurred.

Meat from animals that were fed genetically modified crops do not need to be labeled.

Plant scientists that are pro-GM argue that crops can lead farmers to use fewer environment-killing herbicides and pesticides. They also point out that studies have found that biotech foods are safe. But supporters of the label point out that benefits are temporary, and that there is also evidence that weeds and insects have evolved in response to the modifications.

This month, 69 percent of Californians voted for the measure. But we are still months away from the vote and opinions change. Earlier this year, 67 percent of voters said that they were in favor of a cigarette tax that would fund disease research. The proposition was narrowly defeated. Coincidentally, opponents of the measure spent $50 million in order to make sure of the outcome.