The World Trade Organisation (WTO) has agreed to examine complaints about European restrictions on genetically modified organisms (GMOs), trade officials in Geneva have said.
The complaints - made by the US and backed by Canada and Argentina - argue that European Union (EU) policy on GMOs violates world trade rules.
Since 1998, the EU has not allowed new genetically modified crops to be imported or grown in the 15 EU states.
The EU has denied breaking trade rules.
Change of plan
Nothing is likely to come of the investigation for at least 18 months, the probable length of the three-judge inquiry.
In the meantime, the EU's new policy on GMO-related labelling should have time to bed down.
EU farm ministers agreed last month to move from a blanket ban to a stringent system of labelling when GM ingredients are used either in foodstuffs for human consumption or in animal feed.
But the US says that will still discriminate against its farmers, given the much more widespread use of GMOs in US agriculture.
The vast majority of US soy, for example, is GM.
The US insists that there is no scientific evidence proving damage to either human health or the environment, and that the EU's "precautionary principle" goes too far.
Separately, the WTO said it would also look into complaints against the EU's sugar subsidy regime brought by Brazil, Australia and Thailand.
The three complainants say the EU, the world's largest sugar exporter, helps distorts world prices by supporting its sugar farmers to the tune of billions of dollars.
The EU rejected the complaint.
"We are confident we are in full compliance with WTO rules," said a spokesman for EU agriculture commissioner Franz Fischler.
One plank of the EU's defence is that it helps sugar producers in developing countries by importing sugar at the subsidised EU price.