EGG producers in the UK could lose their free range status if chickens are kept indoors to stop them catching bird flu, the National Farmers' Union (NFU) warned days ago.
The fears come as the Dutch government brings in similar measures to stop commercially farmed poultry catching bird flu from wildfowl.
A strain of the virus has already spread into Russia and there are fears that it could reach continental Europe.
Charles Bourne, the NFU's poultry board chairman, said there was growing anxiety among British poultry farmers as the bird flu spread further west.
"As it creeps across Russia and into Europe it gets more significant," he said.
"Certainly, the financial implications for a farmer whose birds get it is colossal. Farmers would actually be ruined."
Around 5.5m of the Netherlands' 90m chickens will be affected by the Dutch government's measures, which came into force on Monday.
Mr Bourne said farmers would support similar measures but voiced concerns over the impact on free range and organic farmers, who account for around 27 per cent of total egg production.
"It is a question of taking precautions in advance so that we don't get the disease. The problem from the farmer's point of view is that he could lose his free range status," he said.
"Loss of status would mean lost revenue for the producers, many of whom operate on a small scale."
Stephen Throup, who keeps 35,000 free range hens on two separate sites at Nun Monkton, near York, said: "It is obviously very worrying. All we can do is accept the advice we are given."
Mr Throup produces just under 10.5m eggs a year and said egg production accounted for a major part of his income now that milk and arable enterprises had become unprofitable.
He added: "If the birds have to be put indoors and are then classed as barn hens instead of free range the price we receive would drop substantially. We would be in trouble if we lost the free range premium."
David Hugill, who runs a free range egg laying enterprise at Faceby, near Stokesley, said: "The situation is very worrying but if Defra (the Department of the Environment, Food and Rural Affairs) tell us we have to fasten our birds up I would not expect to lose my free range status."
A Defra spokesman said it was not advising action similar to that taken in the Netherlands as it was not yet thought to be proportionate to the risk.
"The risk assessment that vets are recommending to us is still low at the moment but obviously we would remain vigilant," he said.
Animal Welfare Minister Ben Bradshaw also ruled out following the Dutch example. He said that although the risk had "increased a little bit" it was still low.
