Maros Sefcovic, the commission vice president, called on the British government to respect "its worldwide law obligations", saying Brussels would "not be shy" to respond to any unilateral action from London.
Commenting on the same matter, Maroš Šefčovič, European Commission Vice President of Interinstitutional Relations and Foresight, noted that they at a crossroads in their relationship with the UK.
On the same note, David Frost, the British minister responsible for implementing the Brexit deal, said there were no breakthroughs and no breakdowns in N. Ireland Protocol talks with the EU.
'What you have to bear in mind is that the Protocol always envisaged that both parties would show best endeavours to make the Northern Ireland Protocol work, and that included recognising that Northern Ireland was an integral part of the United Kingdom and that you should support the free flow of goods to Northern Ireland, ' he told Sky News.
"When I meet Maros Sefcovic later today my message will be clear: time is short and practical solutions are needed now to make the Protocol work", Frost said.
But the port checks on deliveries heading into Northern Ireland from mainland Great Britain - England, Scotland and Wales - have caused consternation in unionist communities, which maintain this changes their place in the wider UK.
The divorce deal, which took effect on January 1, included a number of grace periods that gave Britain time to put in place new systems to check a variety of goods coming into Northern Ireland to ensure they comply with European Union rules.
The Northern Ireland Protocol was meant to ensure no return to a hard border with the Republic of Ireland.
Checks had to be suspended earlier this year because of threats to port staff, and the protocol was blamed for the worst violence in years in the British-run province.
He said: "Businesses in Great Britain are choosing not to sell their goods into Northern Ireland because of burdensome paperwork, medicine manufacturers are threatening to cut vital supplies, and chilled meats from British farmers destined for the Northern Ireland market are at risk of being banned entirely".
Ahead of talks with Sefcovic in London on Wednesday, Brexit minister Lord Frost called for "pragmatism", in an overnight statement. This work is important. Maros Sefcovic, the EU's chief negotiator, cautioned against such action, saying the two sides should strive to achieve "mutually agreed compliance paths".
The Tory peer, who is a close ally of Boris Johnson, said "pragmatic solutions" must be found and did not rule out unilaterally extending the grace period on chilled meat exports between Britain and Northern Ireland.