Since the British voted to leave the EU five years ago, an old quarrel has flared up.
The conflict is basically about who should be allowed to fish where - both Britain and France want to limit the other person's right to fish in their waters.
The French government is threatening to impose sanctions from Tuesday, which would include stricter controls on British goods.
In addition, they want to ban British ships and boats from docking in certain French ports.
The reason is that it is believed that French fishermen are allocated too few fishing rights off the coast of Great Britain.
In addition, a British fishing boat is being detained in Le Havre, which is said to have fished in French waters without a permit.
"Unreasonable threats"
The French proposal for sanctions has aroused anger in the neighboring country.
In an interview with the television channel Sky News, the British Foreign Secretary Liz Truss calls the planned sanctions "completely unreasonable threats".
- The French have behaved unfairly.
It is not in accordance with the trade agreement, says the Foreign Minister and refers to the British agreement with the EU which regulates trade after withdrawal.
She threatens that Britain can respond with its own measures, within the framework of the trade agreement, if France goes ahead with its sanctions.
- That is what we intend to do if the French do not back down, says Liz Truss.
Fruitless summit
During the G20 summit in Rome last week, the countries' prime ministers, Boris Johnson and Emmanuel Macron, met for just over half an hour to discuss the fisheries issue.
However, they must not have reached a new agreement on fishing.
Earlier, the British summoned the French ambassador to protest France's threats.