The European Union is urging its 27 member states to test certain wheat shipments from the United States after unauthorized genetically modified grains were found on a U.S. farm, officials said Friday.

The move came after Japan halted imports Thursday of some types of wheat from the U.S. following the discovery of an experimental strain that was tested by Monsanto but was never approved.

“The Commission is following carefully the presence of this non-authorized GM wheat in Oregon in order to ensure that European consumers are protected from any unauthorized GM presence and make sure that the EU zero tolerance for such GM events is implemented,” EU’s consumer protection office said.

The agency said it was seeking “further information and reassurance” from U.S. authorities and had asked Monsanto for help in developing a reliable test for GM grains in soft white wheat.

Shipments that test positive should not be sold, but current information from the U.S. Food and Drug Administration indicated the wheat posed no threat to human health, it said.

The European Union imports more than 1 million metric tons (1.1 million tons) of U.S. wheat each year. Eighty percent of that was soft white wheat, the majority of which is exported to Spain, officials said.

European consumers have generally objected more strongly to genetically modified foodstuffs than Americans.