Shellfishermen in Flookburgh, who normally earn much of their income from harvesting mussels and cockles in Morecambe Bay, have been told they can't export them to France until the end of April.
South Lakes MP Tim Farron has written to Environment Secretary George Eustice urging him to intervene.
In his letter Mr Farron said: “I am sure you will agree that this is unacceptable and l request that this is urgently resolved and all affected fishermen are communicated with as soon as possible and are offered every assistance, especially as their normal income has fallen off the cliff edge with no warning and most have families who are reliant on a regular income to survive.”
Bivalves like oysters, clams and mussels have to be purged of contaminants in fresh water before they can be eaten.
Defra said wild harvested molluscs which need purging can't be exported tot he EU until the EU’s new Animal Health Regulations come into force on April 21.
Those that have already been purged are unaffected. A spokesman said they were working to find an interim solution.