The move would extend a ‘grace period’ designed to allow UK supermarkets and suppliers time to adapt to new trade barriers across the Irish Sea.
But Maros Sefcovic, vice president of the European Commission, said that would be a “violation” of the protocol agreed with the UK.
He also warned it would be the “second time that the UK government is set to breach international law”, following a similar row last year.
In a statement the European Commission said Sefcovic would inform Lord Frost, the minister who helped negotiate the Brexit deal, that it would “respond to these developments in accordance with the legal means established by the Withdrawal Agreement and the Trade and Cooperation Agreement.”
It added that the EU had “strong concerns over the UK’s unilateral action, as this amounts to a violation of the relevant substantive provisions of the Protocol on Ireland/Northern Ireland and the good faith obligation under the Withdrawal Agreement.
“This is the second time that the UK government is set to breach international law.
“This also constitutes a clear departure from the constructive approach that has prevailed up until now, thereby undermining … the mutual trust necessary for solution-oriented cooperation.”
The grace period – a temporary relaxation of checks – had been due to expire at the end of this month.
At that point supermarkets in Northern Ireland, which have struggled with supply problems since the government’s Brexit deal came into force on 1 January, had expected to see their woes worsen.
But Northern Ireland secretary Brandon Lewis said the government would be “taking several temporary operational steps to avoid disruptive cliff-edges as engagement with the EU continues through the Joint Committee”.
Controversially he announced the new grace period would continue until at least 1 October.
Ministers had asked the EU to extend the grace period until 2023, but Brussels had declined to do so so far.
Like Brussels, the Irish government has also criticised the UK government’s plans, branding them “deeply unhelpful”.
Irish foreign affairs minister Simon Coveney said unilaterally continuing the grace period undermined the UK’s commitment to the protocol.
He said: “A unilateral announcement is deeply unhelpful to building the relationship of trust and partnership that is central to the implementation of the protocol.”
