Environmental pressure group Friends of the Earth has launched its GM-free Britain campaign.
The campaign aims to encourage local authorities to become genetically-modified free zones.
It was launched as a new National Opinion Poll survey was published showing that 57 per cent of people are opposed to commercially grown GM crops.
Friends of the Earth has asked local authorities to make sure no GM crops are grown on land they control and to adopt a GM-free policy for their services such as school meals.
Friends of the Earth's GM campaigner Pete Riley said: "This is a crucial time in the GM debate. The government will soon decide whether to allow GM crops to be commercially grown in the UK. If it decides in favour it will lead to widespread GM contamination of crops, food and the environment."
At the moment it is a legal requirement for pubs, and other outlets selling food, to label any food that contains GM ingredients.
But although the law exists, and a majority of pubs mark GM food on their menu, many publicans say they have never been asked to prove whether their food-labelling complies with the law.