More than a third of businesses across the UK's food and farming industry would become "unviable" without access to European workers, new research has found.
A report by the Food and Drink Federation (FDF) said 36% of firms in the industry's £110 billion supply chain would see their business models fail if they could not hire EU nationals.
Supported by trade bodies throughout the food, drink and farming industry, the study said 17% of firms would shift their operations overseas in response to a block on EU workers.
The research was sourced from 627 business and included input from the Association of Labour Providers, British Beer and Pub Association, British Hospitality Association, British Retail Consortium, Fresh Produce Consortium and the National Farmers' Union.
To ensure the future of the supply chain, they have called on the Government to secure the rights of European nationals currently living in the UK, review how immigration data is recorded and build an "attractive and effective" migration system.
Ian Wright, director general of the FDF, said: "The UK food and drink supply chain ensures that consumers have access to the safe, affordable and delicious range of food and drink that they have come to expect.
"Food is a matter of national security, so the results of this report are of central concern to businesses across the 'farm to fork' industries.
"It is only a matter of time before the uncertainty reported by businesses results in an irreversible exit of EU workers from these shores. This is a scenario that will hurt the UK culturally and economically.
"Without our dedicated and valued workforce, we would be unable to feed the nation. This is why it is imperative that we receive assurances from Government about their future, and that of our wider workforce."
There are two million EU nationals within the UK economy, 20% of which are working in the food and drink supply chain.
Nearly a half of businesses said EU workers were looking to leave the UK due to uncertainty over their future, according to the study.
Meanwhile, 31% of firms said they had already seen EU nationals depart since the Brexit vote.
It said the sector, which employs four million people across the UK, could not stomach a "cliff edge" and the supply chain would endure "significant disruption" if there was sudden halt in EU workers coming into the industry.
Andrew Opie, director of food and sustainability at the BRC, said: "EU workers are key to getting British food on our shelves. From producing food, through transport to colleagues in store, they are vital in providing the service and quality British consumers demand.
"To deliver a fair Brexit for consumers and tackle uncertainty, EU colleagues currently working in the retail industry and the wider food supply chain need further clarity about their status once the UK leaves the EU."
A Government spokesman said: "After we leave the EU we must have an immigration system which works in the best interests of the UK.
"Crucial to the development of this will be the views from a range of businesses, including the agricultural, food, drink and manufacturing sectors.
"We will be setting out our initial proposals for this system in the autumn but we have already been clear there will be an implementation period after we leave the EU to avoid a cliff edge for businesses.
"In June we published our offer to protect the rights of EU citizens in the UK, confirming no-one living here lawfully will be asked to leave when we exit the EU and they will have a grace period to regularise their status."