Britain's shellfish industry was dealt a "devastating blow" as Brexit regulations meant it had to abandon trade with Europe temporarily.
Environment Secretary George Eustice said on Monday that rules regarding British molluscs meant they cannot be exported to the continent.
He said the situation was unacceptable and had written to the European Commission to ask for the rules to be relaxed.
Europe does not accept molluscs – including mussels, oysters, clams and cockles – from Class B waters, which have not been through purification or have not cleared testing.
This meant EU traders cannot now accept some shellfish caught off the Welsh or Cornish coasts, although molluscs from Class A waters in Scotland are unaffected.
British shellfish farmers had been able to sidestep these regulations while trading under bloc rules, but they must now obey the Class B ban.
Mr Eustice said there was a “long-standing trade in live bivalve molluscs to the EU from UK waters”.
He said this benefited “both our own shellfish industry and EU restaurants and retailers who rely on these premium products from the UK”.
According to Mr Eustice, the EC changed its position last week, and prior to that “they had been clear that this was a trade that could continue”.
"We continue to believe that our interpretation of the law and the EU's original interpretation is correct and that the trade should be able to continue for all relevant molluscs from April," he told parliament.
“Bringing an end to this traditional and valuable trade is unacceptable. I recognise this is a devastating blow to those businesses that are reliant on the trade.”
The introduction of checks and paperwork after Britain's departure from the EU caused widespread disruption to exports of fresh fish and seafood.
Fishers across Britain expressed frustration at a lack of government action.
Last month, seafood hauliers protested against the Brexit fishing deal by parking their lorries in central London.