It is the biggest cash takeover in history - but it’s shrouded in controversy. And on this year's World Food Day - the merger between German chemical giant Bayer and US genetically modified seed firm Monsanto is of increasing concern to campaign groups. Both companies say the deal would be good for everyone. But even some investors are skeptical.

This small group of protesters believes the future of the world’s safe food supply relies on them. They want to stop regulatory approval of the largest corporate cash takeover in history. Their fear: that the TransAtlantic tie-up could significantly speed up the spread of genetically modified crops.

“For the past years, we have been free of this — but not really in the sense that we know what we are eating. In Germany — we are a little bit protected. But there’s still open corners that we — as consumers — have to be aware of." Mauricio Lizarazo Prada, organizer of "March against monsanto".

GM is common in U.S. seed-making company Monsanto’s home turf — where proponents argue such technology could help solve world hunger.But it’s rare on the continent of its buyer — where many question the ethics. Though not German chemical Bayer.

"We believe there’s no reason to ban genetically engineered seeds worldwide. Many farmers buy these seeds and use them successfully for many years, because the new modern types have a range of advantages. And there is no scientific proof regarding the safety of genetically engineered seeds and that there are any risks in connection with the use of green genetic engineering. Green genetic engineering, the technology, is safe."Utz Glages, a bayer spokesperson.

Investors have shown some scepticism too — worrying this 66 billion US dollar deal is bigger than it’s true worth.