"No on 37" is a campaign to defeat "California Proposition 37, Mandatory Labeling of Genetically Engineered Food," which is up for a vote in the November election. I ran across the ad shown here on the LA Times' website and didn't find it particularly persuasive.
When I visited the site I was impressed by processed food conglomerates' desperation to defeat this bill. Monsanto is one of the corporations spending money to defeat 37 (According to Yes on 37, Monsanto, DuPont, Bayer, Dow, BASF and Syngenta have donated $19 million to No on 37). Why does it care? Could it be because a peer-reviewed health study revealed massive tumors in rats fed Monsanto’s genetically engineered corn? (UPDATE: Thanks to the commenters who linked to articles critical of the study. The study sounds very problematic, I mainly thought the ad was dumb.)
Here's a list of companies in favor of Prop 37.