The World Trade Organization is investigating the European Union's refusal to accept most genetically modified organisms (GMOs).
The United States, backed by Canada and Argentina, says that the Europeans, who have not allowed new genetically modified crops to be imported or grown in the EU's 15 member states since 1998, have shown no willingness to end the embargo.
But the EU denies that it is in breach of WTO rules. The investigation, which will begin with a ruling by a panel of three trade judges, could take up to 18 months.