EU nations refused to back a limited extension of the herbicide glyphosate's use on Monday, threatening withdrawal of Monsanto's Roundup and other herbicides from shelves if no decision is reached by the end of the month.
Contradictory findings on the carcinogenic risks of the chemical have thrust it into the center of a dispute among EU and U.S. politicians, regulators and researchers.
The EU executive - after failing to win support in two meetings earlier this year for a proposal to renew the license for glyphosate for up to 15 years - had offered a 12 to 18 month extension to allow time for further scientific study.
It hopes a study by the European Chemicals Agency (ECHA) will allay health concerns, as citizen and environmental groups pile pressure on governments to take a precautionary approach.
The compromise proposal failed to win the qualified majority needed for adoption, an EU official said, adding the European Commission will discuss the issue at a meeting on Tuesday.
Seven member states abstained and 20 backed the proposal, a German environment ministry spokeswoman said. Only Malta voted against, diplomats said.
Without a majority decision, the EU executive may submit its proposal to an appeal committee of political representatives of the 28 member states within a month. If there is again no decision, the European Commission may adopt its own proposal.
The controversy hangs over German chemicals group Bayer's $62 billion offer in May to buy U.S. seeds company Monsanto. Germany was among states which abstained on Monday and has opposed Monsanto's genetically modified seeds.
For Monsanto, glyphosate use is most important in the United States and Brazil, where the U.S. group depends on the sale of genetically modified crops that resist the glyphosate weedkiller.
In Europe, genetically modified seeds face strong opposition and play virtually no role in commercial farming but a refusal of a new license for glyphosate there could signal stricter regulation of the broader agricultural chemicals industry.
Such a move by the EU might also stoke the glyphosate debate in other world regions.
Monsanto has not ruled out a legal appeal if approval lapses after June 30, requiring a six-month phase-out of glyphosate-containing products, and the industry lobby has criticized the regulatory uncertainty.
"With this decision all they do is cast doubt on that system, and create fear and confusion amongst Europe's consumers," Graeme Taylor of the European Crop Protection Association said.
Environmental and citizen campaign groups have called for an EU-wide ban in the absence of scientific certainty.
"Extending the glyphosate license would be like smelling gas and refusing to evacuate to check for a leak," Greenpeace EU food policy director Franziska Achterberg said in a statement.
The prospect of a European ban could complicate EU-U.S. trade talks. The issue is being closely watched by regulators on the other side of the Atlantic.
The U.N.'s Food and Agriculture Organization (FAO) and World Health Organization (WHO) said in May glyphosate was unlikely to pose a risk to people exposed to it through food.
The finding matches that of the European Food Safety Authority (EFSA), an independent agency funded by the European Union, but runs counter to a March 2015 study by the WHO's Lyon-based International Agency for Research on Cancer (IARC).
That agency said the chemical was probably able to cause cancer and classified it as a 'Group 2A' carcinogen. It assessed whether the substance can cause cancer in any way - regardless of real-life conditions on typical levels of human exposure or consumption.