At a private meeting in Rome on Sunday during the G20 summit, Mr Johnson told French President Emmanuel Macron that France must “withdraw their threats”.
If not, London has made clear that retaliatory action would be taken.
Speaking at a press conference later, the Prime Minister also declared himself “puzzled” by a letter from Jean Castex, the French prime minister, “explicitly asking for Britain to be punished for leaving the EU”.
Mr Johnson said: “I just have to say everybody, I don’t believe that that is compatible either with the spirit or the letter of the Withdrawal Agreement or the Trade and Cooperation Agreement.”
The UK Government believes the move breaches commitments in the UK-EU treaty to act in “good faith”.
Relations between the UK and EU are at risk of deteriorating further, with the Government warning it could trigger Article 16 to suspend parts of the Northern Ireland protocol unless both sides can bridge “significant gaps” to break the deadlock .
Negotiations could yet break down
Mr Sefcovic, the EU’s lead negotiator, warns that negotiations over the protocol, which created a customs border in the Irish Sea, could yet break down because the bloc has “limits” on how far it can compromise.
He said: “With the EU’s package of enhanced opportunities from this October, we have gone the extra mile. But we have our limits, too, as we must protect the integrity of the EU’s Single Market and the interest of the 27 member states.”
Lord Frost is calling for the European Court of Justice to be stripped of its powers to police the EU rules used to avoid a hard border with Ireland – despite the Commission insisting the role of European judges is “not up for discussion”.
The EU has proposed cutting the number of checks on British goods entering Northern Ireland by up to 80 per cent, but the Government has said the bloc’s concessions do not go far enough to end disruptions caused by the protocol.
Ongoing fishing row
The Prime Minister’s public intervention in the ongoing fishing row came after No 10 rejected Paris’s claims that Mr Johnson and Mr Macron had reached an agreement in their private meeting.
Downing Street hit back after a senior French official was quoted by Bloomberg as saying Paris and London were on track to de-escalate the spat.
Instead, a spokesman for the Prime Minister said that Mr Johnson had used the meeting to personally stress “his deep concern over the rhetoric emanating from the French Government in recent days”, including the letter sent by Mr Castex.