China rejected a shipment of U.S. corn late last week after officials learned that it contained an unsanctioned strain of the genetically modified commodity. The action, which would be the country’s first refusal of U.S. corn, could further strain U.S.-China trade relations.

“China only allows 11 varieties of GM corn to be imported to the country, and the cargo was found with GM material outside the 11 varieties,” an anonymous source told Reuters.  “The animal and plant quarantine department has barred it from entering China.”

According to the international wire service, the shipment was somewhere between 50,000 and 60,000 tons.

China’s demand for U.S. corn has soared this year due to the country’s increased meat production, which utilizes corn-based feed. China’s corn supply this year was not adequate to meet its growing demand.