The European Union threatened legal action against the United Kingdom on Monday after the latter's government proposed legislation that suggests a unilateral overhaul to the post-Brexit trade deal it signed for Northern Ireland.      

European Commission Vice President Maros Sefcovic stated to reporters in Brussels that "It is with significant concern that we take note of today's decision by the UK Government to table legislation," adding that "Unilateral action is damaging to mutual trust. The Commission will now assess the UK draft legislation."    

Sefcovic handles the EU's fraught ties with the UK government.

The Europeans would not renegotiate the divorce deal and its special protocol for trade in Northern Ireland, he said, and this "will simply bring further legal uncertainty for the people and businesses in Northern Ireland."      

Considering the breach of the deal, Sefcovic said that Brussels would consider reopening a suspended "infringement procedure" against the UK, in addition to opening fresh cases to "protect the EU single market from risks that the violation of the protocol creates for the EU businesses and for the health and safety of EU citizens", he added.      

The protocol requires checks on goods coming to Northern Ireland from England, Wales, and Scotland, in order to track those that could possibly be going to the EU via Ireland.      

This creates a customs border down the Irish Sea, keeping Northern Ireland in the customs orbit of the EU to avoid a politically sensitive hard border with Ireland.   

Sinn Fein: UK set to break int'l law with new N. Ireland trade laws

Britain will be breaking international law by passing legislation that will unilaterally change the protocol of North Ireland that rules trade post-Brexit, according to Mary Lou McDonald, the president of Ireland's Sinn Fein party.

McDonald said there were mechanisms to improve applying the protocol involving trade between Ireland and Belgium. 

"There is a willingness here, there is a willingness to engage by the European Commission, but the British government has refused to engage," she told Sky News.

"It has not been constructive, it has sought a destructive path, and is now proposing to introduce legislation that will undoubtedly breach international law."

PM Johnson using N. Ireland against EU: Sinn Fein leader

UK Prime Minister is playing games with Ireland and using it as a pawn in the country's ongoing trade battle with the European Union following the Brexit deal, Sinn Fein leader Mary Lou McDonald said last month. 

McDonald accused the premier of being in "cahoots" with the pro-London party stopping an executive and assembly sitting.

The Stormont by-laws stipulate that a new administration only be formed without the largest unionist party taking part.

"He has connived with the DUP to use Ireland, the north of Ireland, to use unionism in Ireland as a pawn in a wider game that is being played out with the European Union," McDonald said in reference to Johnson.

She went on to call his tactic and approach "shameful" and "absolutely not acceptable."

"It is very clear that the Tory government in London is in cahoots with the DUP to stall and to hold back progress, to frustrate the will of the people as expressed in the election, and that, to anybody who calls themselves a democrat, is clearly unacceptable and clearly shameful. And that case will be made to Boris Johnson," she stressed.

Following the latest election, the DUP became Northern Ireland's second-largest party, losing the seat it had kept since the formation of Northern Ireland in 1921.