The British government has unilaterally said the grace period for post-Brexit supermarket agri-food movements from the rest of the UK to Northern Ireland "will continue" until October.
The move was announced in the House of Commons this morning by Northern Ireland Secretary Brandon Lewis.
He added that certification requirements will then be introduced in phases alongside the roll out of a digital assistance scheme.
Businesses in Northern Ireland have been pressing for an extension to avoid a cliff-edge plunge into extra bureaucracy linked to the Northern Ireland Protocol.
Mr Lewis said: "As part of the pragmatic and proportionate implementation of the Northern Ireland Protocol, the government is taking several temporary operational steps to avoid disruptive cliff edges as engagement with the EU continues through the Joint Committee.
"These recognise that appropriate time must be provided for businesses to implement new requirements, and support the effective flow of goods between Great Britain and Northern Ireland."
However, the move has been criticised by the Irish Government and the European Commission.
The EU has said the UK's unilateral move on the Northern Ireland protocol is a potential breach of international law, and contrary to the good faith provision of the Brexit Withdrawal Agreement.
In a strongly worded statement, the vice-president of the European Commission, Maros Šefcovic referred to the UK's Internal Market Bill, introduced last September, which breached the Protocol.
Mr Šefcovic said: "This is the second time that the UK government is set to breach international law."
Last week, following a meeting of the EU UK Joint Committee, Mr Šefcovic and his then UK counterpart Michael Gove issued a statement, acknowledging "the importance of joint action to make the Protocol work for the benefit of everyone in Northern Ireland."
That statement added: "In that spirit, the EU and UK reiterated their full commitment to the Good Friday (Belfast) Agreement in all its dimensions, and to the proper implementation of the Protocol."
In his statement tonight, Mr Šefcovic said the latest UK move "constitutes a clear departure from the constructive approach that has prevailed up until now, thereby undermining both the work of the Joint Committee and the mutual trust necessary for solution-oriented cooperation."
He accused the UK of not informing him of the move in advance, saying all issues relating to the Protocol "should be dealt with through the structures provided for by the Withdrawal Agreement".
Mr Šefcovic spoke this evening to David Frost, who took over from Michael Gove as co-chair of the Joint Committee and of the EU-UK Joint Partnership Council.
He said the European Commission would respond to the latest UK move "in accordance with the legal means established by the Withdrawal Agreement and the Trade and Cooperation Agreement".
Mr Frost told Mr Šefcovic that the UK's unilateral action was "temporary and technical steps" which "largely" continued measures already in place.
According to a readout following a call between the two, Mr Frost said these were the "minimum necessary steps" to avoid more disruption to Northern Ireland.
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.
"He underlined that these were needed for operational reasons and were the minimum necessary steps to allow time for constructive discussions in the Joint Committee to continue without the prospect of disruption to the everyday life of people in Northern Ireland in the coming weeks.
"He noted that such operational measures were well precedented in other international trade arrangements and that they were entirely consistent with our intention to discharge our obligations under the Protocol in good faith."
Taoiseach 'disappointed' over 'unilateral action'
Taoiseach Micheál Martin said he was "disappointed" with the British government's "unilateral action".
He said: "Issues relating to the protocol should be resolved by the UK and EU working together, through the Joint Committee.
"We have worked continuously in support of efforts to find sensible means of implementing the Protocol that respond to challenges identified.
"We will continue to do so, but unilateral action undermines the trust necessary to reach agreement.
"I call on the British Government to engage urgently with the European Commission, and to work towards agreed outcomes."
Checks on goods at Northern Ireland's Irish Sea ports were agreed between Northern Ireland and the EU, to avoid a hard border on the island of Ireland and keep the region following the bloc's trade rules.
That has caused some disruption to Irish Sea trade and prompted a backlash from unionists who fear it threatens Northern Ireland's place in the UK internal market, with the DUP aiming to undermine the protocol.
Mr Lewis said: "For supermarkets and their suppliers, as part of the operational plan the UK committed to at the UK-EU Joint Committee on February 24, the current Scheme for Temporary Agri-food Movements to Northern Ireland (STAMNI) will continue until October 1.
"Certification requirements will then be introduced in phases alongside the rollout of the Digital Assistance Scheme."
He said further guidance will be provided later this week on parcel movements from Great Britain to Northern Ireland, to provide necessary additional time for traders beyond 1 April.
"Guidance will also be set out to help address practical problems on soil attached to the movement of plants, seeds, bulbs, vegetables and agricultural machinery," Mr Lewis said.
The first of the grace periods had been due to expire at the end of March. Supermarkets would have had to produce Export Health Certificates for all shipments of animal products.
Under the terms of the protocol, which governs the movement of goods in and out of the region post-Brexit, all non-prohibited agri-food goods arriving from GB require an EU export health certificate (EHC) declaring that they pose no risk.
They are a consequence of a Brexit deal that has resulted in Northern Ireland remaining in the EU single market for goods, while the rest of the UK has left that regulatory zone.
There are hundreds of different types of EHCs, with different forms for different products and some products having multiple certificate versions.
A UK government spokesperson said: "We are committed to meeting our protocol obligations in a pragmatic and proportionate way, but there have been challenges that are having a direct, and often disproportionate, impact on lives and livelihoods, including an unacceptable disruption to the flow of critical goods.
"That is why, as part of our new operational plan for supermarkets and their suppliers, underpinned by the Digital Assistance Scheme to enable goods to be moved in accordance with the protocol in the most streamlined way possible, we will extend the existing arrangements to October to reflect the reality that it takes time to adapt and implement new requirements."
DUP Stormont Agriculture Minister, Gordon Lyons, sparked controversy on Friday night when he announced he had ordered officials to halt work on planned permanent facilities to carry out inspections on goods from Great Britain.
Rival politicians have accused Mr Lyons of stunt politics and have insisted he does not have the authority to act unilaterally on issues considered significant or controversial.
Sinn Féin, the SDLP and the Alliance Party have made clear such decisions can only be taken by the Executive as a whole.
Today's solo run from the British government was completely unnecessary, totally undermines the work of the Joint Committee and puts it on an immediate collision course with the EU #Brexit #IrishProtocol— Mary Lou McDonald (@MaryLouMcDonald) March 3, 2021
The Northern Ireland Retail Consortium welcomed the news.
"The retail industry welcomes the extension of the grace periods in both time and scope, even if it is unilaterally, to allow us to continue to give Northern Ireland households the choice and affordability they need.
"We now have short-term stability, one of our four key asks. But there is still much to be delivered," said chief executive Aodhán Connolly.
Additional reporting Tony Connelly