Produce like Welsh lamb and Halen Mon salt could lose their protected status if Britain leaves the EU, Plaid Cymru has said.
EU rules mean certain approved foods - from champagne to Cornish pasties - can only be produced in certain locations.
Plaid, campaigning to stay in the EU, said without the protection lower-quality food could be made elsewhere.
But Vote Leave, leading the campaign to leave the EU, said the argument was "absolute nonsense".
Voters will decide in a referendum on 23 June whether Britain remains a member of the 28-country union, or leaves.
Plaid AM Simon Thomas said: "One of the benefits of European Union membership is the protected status of specialist Welsh foods.
"These special designations mean that Welsh lamb or Halen Mon can only be made here in Wales, and our producers don't have to compete with cheap imitations."
But Vincent Bailey, a spokesman for Vote Leave Cymru, said: "These claims are absolute nonsense because protected food status works both ways.
"The UK would ensure that our products were protected in the EU by striking a new deal, it's as simple as that. And the EU would want to strike a deal to protect their own products in the UK from unfair competition from inferior products."