The British government has been accused of breaking international law for a second time by the European commission after ministers said the UK would unilaterally act to give Northern Ireland businesses time to adapt to post-Brexit rules. In a damning statement, Maroš Šefčovič, the vice-president of the commission, said a move announced by Northern Ireland secretary Brandon Lewis to exempt goods coming from Great Britain from checks amounted to a “violation” of the withdrawal agreement. “This is the second time that the UK government is set to breach international law,” the statement said. “This also constitutes a clear departure from the constructive approach that has prevailed up until now.” Lewis announced a “new operation plan” for sending goods from Great Britain to Northern Ireland to the Commons on Wednesday. The UK has asked for a two-year extension to all grace periods for Irish Sea border checks including those on food, parcels, plants and medicines, but so far Brussels has resisted. Lewis said the government had to act to protect the interests of Northern Ireland and keep shelves stocked. “We are taking forward a series of further temporary operational steps which reflect the simple reality that there is more time needed to adapt and implement new requirements as we continue our discussions with the EU,” he said. The commission said it had not been informed of the decision in advance of Lewis informing parliament and suggested the move would be a hammer-blow to trust between the two sides after an already bruising period. The two sides have been seeking to rebuild relations on the joint committee responsible for implementing the withdrawal agreement, although Michael Gove has recently been replaced by Lord Frost, the former Brexit trade negotiator, who has a record for upsetting the EU side with his robust stance. It was Lewis who told the Commons last year that the government intended to break international law in a “limited and specific way” in the later ditched internal market bill overriding parts of the Brexit withdrawal agreement. The decision then drew outcry, including a warning from the then US presidential hopeful Joe Biden about the need to respect the Good Friday Agreement. The commission statement said: “It is equally disappointing that the UK government has resorted to such unilateral action without informing the EU’s co-chair of the joint committee. Issues relating to the Protocol should be dealt with through the structures provided for by the Withdrawal Agreement. Šefčovič later spoke to Frost on Wednesday evening to inform the British cabinet minister that the EU would “respond to these developments in accordance with the legal means established by the Withdrawal Agreement and the Trade and Cooperation Agreement”. According to a readout issued by Downing Street of the call between the pair, Frost had described the measures as “well precedented” and “entirely consistent with our intention to discharge our obligations under the protocol in good faith”. A UK government spokesperson said: “Lord Frost explained that the measures announced today, following official-level notification to the commission earlier this week, were temporary technical steps, which largely continued measures already in place, to provide more time for businesses such as supermarkets and parcel operators to adapt to and implement the new requirements in the protocol.” The row is a remarkable new battle over the Northern Ireland protocol, the part of the Brexit deal that keeps Northern Ireland a part of the EU’s single market for goods. Boris Johnson threw his weight behind the announcement and told MPs Northern Ireland’s position within the UK internal market was “rock-solid and guaranteed”. He said the government would reinforce that with operational “easings” to protect food supplies and other areas, pending further discussions with the EU. Checks on goods arriving from Great Britain have disrupted supply chains and triggered protests from Northern Ireland’s unionist parties, which say the protocol undermines the region’s status in the UK. EU and British leaders have held talks to ameliorate disruption but failed to break the impasse. Last week, both sides pledged to reach a “pragmatic solution”, with the UK agreeing to develop new plans to respond to problems with supermarket supplies. Lewis’s statement to the Commons made no mention of the EU agreement but later said he would hold an informal meeting with Šefčovič. Grace periods have delayed full application of checks. The first of those periods is to expire at the end of March, which will trigger more stringent checks on food and parcels and probably louder protests from unionists. The Northern Ireland Retail Consortium welcomed the news. “We welcome the extension of the grace periods in both time and scope, even if it is unilaterally, to allow us to continue to give NI households the choice and affordability.” Disruption to supermarket and parcel deliveries and the continued refusal of some high street chains to deliver in Northern Ireland have heightened tensions among loyalists and unionist parties who have vowed a campaign of peaceful resistance. The DUP agriculture minister, Gordon Lyons, has halted work on permanent post-Brexit border control posts in Northern Ireland. Existing temporary border posts continue to operate.