BRUSSELS (Reuters) - Online campaigns group Avaaz has called on European Union antitrust regulators to block Bayer’s purchase of Monsanto, saying it would hurt innovation and competition and push up prices.

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The $66 billion deal, the last of three mega takeovers in the sector, has faced criticism from environmental and agricultural groups as well as lawmakers on both sides of the Atlantic, concerned about the combined entity’s market share.

Avaaz said in a letter to European Competition Commissioner Margrethe Vestagerhad that more than one million people had signed its petition opposing the merger of the German and U.S. companies, which it said would have a major impact on farmers.

“It would control more than one-fourth of the combined global market for seeds and pesticides and lock farmers ever tighter into a supply chain for products that threaten biodiversity and food security by creating dangerous, genetically modified and pesticide-addicted monocultures,” Avaaz lawyer Nick Flynn said in the letter.

The European Commission, whose preliminary review of the deal will end on Aug. 7, did not immediately respond to a request for comment while Bayer said: “The combination of Bayer and Monsanto will enable us to offer farmers more and better solutions through complementary technologies, products and geographic expertise.”

U.S.-incorporated Avaaz, which is funded by its members, is active in climate change, poverty, conflict and corruption issues.

Bayer has been bracing for a full-scale EU investigation. In May it said it expected to close the deal by the end of the year, suggesting it expects a four-month probe at the end of the EU’s initial scrutiny.

The company has agreed to sell its Liberty herbicide and LibertyLink-branded seeds businesses to address regulatory concerns. Both compete with Monsanto’s Roundup weed killer and Roundup Ready seeds.

Dow only secured regulatory clearance to acquire DuPont after pledging to sell key research and development activities and other major assets.

And ChemChina [CNNCC.UL] had to sell a large chunk of its subsidiary Adama’s pesticide, herbicides and insecticides business, its seed treatment products for cereals and sugar beet and a substantial part of its plant growth regulator business for cereals to win EU approval to buy Syngenta.