Russia has suspended the import and use of an American GM corn following a study suggesting a link to breast cancer and organ damage.
Separately, the European Food Safety Authority(EFSA), has ordered its own review in to the research, which was conducted at a French university.
The decision by Russia could be followed by other nations in what would be a severe blow to the take-up of the controversial technology.
Historically, biotech companies have proved the safety of GM crops based on trials involving feeding rats for a period of 90 days.
However, experts at the University of Caen conducted an experiment running for the full lives of rats – two years.
The findings, which were peer reviewed by independent experts before being published in a respected scientific journal, found raised levels of breast cancer, liver and kidney damage.