Stacy Malkan, with the group supporting Prop 37, says consumers have the right to know what's in the food they're eating.
MALKAN: "This is America, it's a democracy, it's a free market system, and the way it's supposed to work is we give people the information so consumers can make informed choices about what we buy and eat."
But Kathy Fairbanks who speaks for opponents of Prop 37 says if it were just about labeling, then why only label some foods? Restaurant foods, alcohol and meat or milk from animals that ate genetically engineered crops don't have to be labeled.
FAIRBANKS: "It also will result in lawyers having a new avenue
to file shakedown lawsuits against everyone on the food chain from
the grocery store all way down to the family farmer."
A UC Davis study -- in part funded by the No Campaign -- found the initiative would cost California food processors about a billion dollars annually. The study suggests many food companies will likely swap out genetically engineered ingredients like corn syrup and soybean oil to avoid a label. And farmers may have to change what seeds and methods they use.
But Prop 37 supporter and organic rice farmer Grant Lundberg says that's part of running a business.
LUNDBERG: "I've been raised to listen to my consumer. This is what they want. You may not agree, but that's the market."
Prop 37 could also have huge ramifications for companies that sell genetically engineered seeds and the herbicides used with them. Monsanto and Dow have contributed millions to the No campaign, which has raised over $34 million.
Proponents of the labeling, including organic food companies, have raised close to $5 million.
Money on both sides is coming in from all over the country because what Californians decide this November will very likely have ripple effects for food companies and consumers across the nation.