The campaign to stop GMO labeling in CaliforniaPhotos by Hugo Felix, Africa Studio / Shutterstock.

As the battle to get genetically engineered foods (or GMOs) labeled in California — a battle that could very well have an impact on labeling nationwide — heats up, Big Food and Big Ag are working in concert to push back to the tune of $25 million. The fight centers around Proposition 37, the ballot initiative from the Right to Know Campaign that will go to vote in November.

If it passes, the result would be no small change. As Mother Jones’ Tom Philpott wrote recently:

Since GM corn, soy, sugar beets, and cotton (the oil part) are processed into sweeteners, fats, and other additives that suffuse the US food system, the initiative would require the labeling of something like 80 percent of all non-organic processed food sold in supermarkets.

As you can see in the chart below, The “Big 6” pesticide makers (BASF, Bayer, Dow, Dupont, Monsanto, and Syngenta) are putting up big money — especially Monsanto and Dupont (full name E. I. Dupont de Nemours). That’s because all of the Big 6 either produce GMO seeds themselves, or pesticides that work in concert with the seeds, so they have the biggest vested interest in seeing GMO proliferation fly under the radar of most Americans.

The names behind processed foods are also getting in on the fight — like PepsiCo, whose many sub-brands sell many foods and beverages that contain GMO high-fructose corn syrup, soy lecithin, etc. So are the companies behind quite a few “health food brands” — from Kashi to Gardenburger to Silk. In fact, the Cornucopia Institute just released a handy shopping guide to help eaters keep their dollars from going to help oppose Prop 37.

Where is the money going, exactly? Many of these companies are paying the same consultants who worked for the tobacco industry to create “astroturf,” or fake grassroots groups that will do their best to make it look like there’s a big crowd of citizens who think labeling is a bad idea. And they’ll undoubtedly convince many voters. This Reuters article that ran yesterday predicts a close battle.

Here’s a breakdown of the 20 largest donors as of Wednesday, Aug. 15:

Chart of funding for anti-GMO labeling campaign

Data source.