The UK government has tabled legislation at Westminster to override parts of the Northern Ireland Protocol.
It seeks to remove some post-Brexit trade barriers for goods moving into Northern Ireland from Great Britain.
The legislation has faced strong opposition from the European Union, claiming that it breaches international law.
But the British government argues the bill is necessary to address problems with Irish Sea trade and help restore a power-sharing government at Stormont.
Here is our guide to the legislation and what to look out for as the deepening political row develops.
What is the Northern Ireland Protocol?
It is a trading arrangement agreed between the UK and EU to prevent a hard land border between Northern Ireland and the Irish Republic after Brexit.
The deal effectively sees Northern Ireland remain in the EU single market for goods with regulatory and customs checks enforced at the region's ports.
But this has introduced red tape on trade moving from Great Britain to Northern Ireland, causing issues for some businesses.
The deal has also angered unionists who claim the region's place within the UK has been undermined.
The DUP has blocked the formation of a new Stormont Assembly and power-sharing Executive following May's Assembly election in protest.
Protracted negotiations between London and Brussels to rework the Protocol have been rumbling on since last year, with both sides tabling proposals but failing to reach a consensus.
The UK government has now embarked on somewhat of a solo run, proposing to remove aspects of the Protocol by way of domestic legislation at Westminster.
What will the new Protocol law do?
The Northern Ireland Protocol Bill aims to ease Irish Sea checks by creating green and red lanes for trade.
The green lane, which would be for goods moving from Great Britain into Northern Ireland and staying in the region, would have no checks and minimal paperwork.
The red lane would be for goods moving through Northern Ireland and onwards to the Irish Republic or wider EU. This lane would retain the checks and inspections required by the Protocol.
A "dual regulatory system" would be introduced, allowing businesses selling in Northern Ireland to choose whether they comply with EU standards, UK standards or both.
The bill would change rules on state subsidies and VAT and excise duties to ensure Northern Ireland is not excluded from UK-wide policy decisions in these areas as a result of EU laws.
The government also wants to remove the European Court of Justice as the final arbitrator in any future trade disputes over the Protocol, instead establishing an "independent arbitration" system.
Are the proposals legal?
Critics of the UK government plans claim the unilateral move against the Brexit treaty by way of domestic legislation is a breach of international law.
However, the government insists it is acting within the law.
It has cited the "doctrine of necessity", arguing this concept justifies setting aside obligations in international treaties under "certain, very exceptional, limited conditions".
The government has also referenced Article 16, a clause in the Protocol that allows either side to take safeguarding measures if the trading arrangements lead to serious economic, societal or environmental difficulties that restrict trade.
Is this all about trade and Stormont?
Sceptics argue the move is more about internal tensions in the Conservative Party than helping Northern Ireland.
With Boris Johnson's leadership under pressure following last week's no-confidence vote, critics argue the Prime Minister is pandering to Brexit hardliners within his party.
Others claim Foreign Secretary Liz Truss's own leadership ambitions may be a factor in her approach to the EU on the Protocol.
The UK government claims the Protocol has upset the Good Friday Agreement's “delicate balance” between unionists and nationalists by undermining the east/west dynamic, citing the lack of support for the arrangements from unionists.
But critics argue the government displayed no such concern about the implications of Brexit when a majority in Northern Ireland voted to remain in the EU in the 2016 referendum.
How will the EU respond to the bill?
Brussels has fiercely criticised the UK government for taking unilateral action.
There are concerns the dispute could eventually spiral into a full-blown trade war.
However, there appears to be little appetite for such an escalation, especially while international focus remains on the cost-of-living crisis and the war in Ukraine.
Instead, the EU is expected in the short-term to resume legal action it had taken against the UK last year over allegedly breaching the terms of the Protocol.
The legal action had been paused in a bid to facilitate negotiations, but any further talks appear unlikely to reach a breakthrough during the current tensions.
Will the DUP now restore Stormont?
Foreign Secretary Liz Truss has urged the DUP to "get on with it" and restore Stormont after the UK government tabled its legislation to override the Protocol.
But DUP leader Sir Jeffrey Donaldson has said they need to see the bill "moving forward" through Westminster before taking any steps to end their veto on re-establishing the Stormont Assembly or Executive.
The Lagan Valley MP previously said the DUP would take a "graduated and cautious" approach, suggesting the party could return incrementally.
Perhaps this could mean firstly agreeing to nominate a Speaker to allow the Assembly to sit, and then at a later stage nominating ministers to Executive positions.
However, the DUP will be cautious about relying on the promises of Boris Johnson, who previously pledged never to agree to a Brexit deal that created economic barriers in the Irish Sea.
Will the Protocol legislation be enacted?
While the Tories have a parliamentary majority, nothing suggests enacting this legislation is guaranteed or straightforward.
Boris Johnson faces pressure within the Conservative Party from Brexit hardliners on one side and those much less keen on picking a fight with the EU on the other.
If dissatisfied, both camps may feel emboldened to rebel - especially as the scale of last week's no-confidence vote against the Prime Minster has precariously weakened his leadership.
It means it could take months for the bill to progress through parliament.
Even if the legislation is enacted, it is possible the sweeping powers potentially bestowed on ministers may never be used.
Sceptics argue the legislation is simply a negotiating ploy by the UK government in a bid to win further concessions on the Protocol from the EU.
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