Oxfordshire's council leaders have voted that the county should be completely free of genetically modified crops.
Friends of the Earth have campaigned against GM crops
Though not legally binding, the council vowed to do all it could to stop GM crops being grown in the region and ban GM food from being served in schools.
Before the debate, Oxford Friends of the Earth had demanded the council use a European law to declare the county GM free.
But farmers already involved in the experiments say it is too late to stop.
The environmental pressure group claim the proliferation of GM crops would lead to widespread contamination of food, conventional crops and the environment.
A council spokesman said: "The county council doesn't have any legal powers to stop people growing GM crops.
"The council has taken a view on GM crops, and is doing all in its power to ensure that Oxfordshire is GM free."
Andrew Wood, food campaigner for Oxford Friends of the Earth said: "This really is of benefit to both wildlife and the agricultural economy of the County."
"However the council executive is being very cautious in its commitment to using its EU powers to stop commercial GM growing in the County."
Friends of the Earth claim a new EU law allows the council to ban a GM crop being grown in a certain geographical area.
A spokesman for the Department for the Environment Food and Rural Affairs denied this, saying the law had never been used in this way, and they did not think it ever would be.