The European Union is taking legal action against the UK following its unilateral decision to ease the terms of the Northern Ireland Protocol, the bloc announced on Monday. 

The new checks in the Irish Sea between Britain and Northern Ireland causing trade disruption, and their subsequent removal by Boris Johnson's government, have increased tensions between the EU and the United Kingdom.

The European Commission has issued a letter to the British government as a formal notice that it had breach EU law, which could cause the European Court of Justice to impose a fine on the UK. 

Earlier in March, the United Kingdom had decided to extend a grace period on new rules for exports from the British mainland to Northern Ireland without seeking the EU's approval.

The two sides fell out over the issue last year, when British ministers re-wrote UK law linked to the Brexit divorce treaty that would have given them powers to ditch large parts of the agreement relating to the province. 

A senior European Commission source, speaking on the condition of anonymity, accused the UK of "a second violation of international law on the same issue."

"This undermines trust and undermines an understanding that we can build a trustful relationship," the official added.

The source said the EU executive has made clear that it would be "willing to show further flexibility on this issue."

"And yet, the response of the UK government is to take unilateral action."

But a British government source said that "all sides need to keep in mind the fact that the [Northern Ireland] Protocol depends on cross-community consent and confidence if it is to work."

They added that it is not "something that should warrant legal action."

The White House waded into the row later on Monday, telling Britain and the European Union to preserve the Good Friday Agreement that Washington helped broker in 1998.

"We continue to encourage both the European Union and the UK government to prioritise pragmatic solutions to safeguard and advance the hard won peace in Northern Ireland," said White House spokeswoman Jen Psaki.

What is the Northern Ireland Protocol?

Since 1998, a Northern Ireland peace accord known as the Good Friday Agreement stipulated keeping the land border open between the Republic of Ireland, which is part of the EU, and Northern Ireland, part of the UK. 

Protecting the Northern Ireland Protocol was part of the Brexit negotiations, which resulted in drafting the Northern Ireland Protocol. 

Under the protocol, Northern Ireland is granted a special status, as it remains in the EU's single market for agrifoods and manufactured goods and stays with the EU's customs union.

This meant that checks on such goods bound for Northern Ireland from the rest of Britain — no longer a part of the single market — would be subject to additional checks and paperwork.

Northern Ireland also still benefits from any post-Brexit trade agreements that the UK strikes with other countries.

What is the problem with the Brexit checks?

After Brexit implementation on January 1, supermarket shelves across Northern Ireland witnessed significant shortages of fresh produce. 

Several British companies were not prepared for the Brexit paperwork to export to Northern Ireland under the terms of the Protocol. 

Some British firms even halted export to Northern Ireland and the EU, citing border complications.

The EU imposes restrictions on the import of certain products from countries outside the bloc, including the UK as a result of Brexit. 

fb/msh (AP, Reuters)