As the United Kingdom and European Union try to solve their Brexit-related trade disputes over Northern Ireland, UK ministers have implied the country could invoke a measure of last resort.
That would mean acting under Article 16 of the Northern Ireland Protocol to unilaterally impose "safeguard" measures to fix a problem in trade.
It comes as the UK government says the protocol has led to disruptions in trade and shortages, leading them to propose a "new legal text" to replace the protocol, arguing that it had "lost consent" in Northern Ireland.
But the EU has indicated that they do not want to renegotiate a protocol agreed with London just two years ago.
As the two parties continue to debate the trade agreement, here's a look at the protocol and its safeguards clause.
What is the Northern Ireland Protocol?
The Northern Ireland Protocol was a part of the European Union and United Kingdom's Brexit agreement.
Designed to prevent a border on the island of Ireland, it prevents checks on goods coming from Northern Ireland (part of the UK) into the Republic of Ireland (part of the EU) in an effort to preserve the 1998 Good Friday Agreement, which ended decades of sectarian violence in Ireland.
But it means that Northern Ireland must follow the rules of the EU's single market, resulting in checks on certain goods coming from England, Scotland and Wales into Northern Ireland.
This has led to protests from unionists in Northern Ireland who say the protocol weakens ties with the rest of the UK and has created shortages.
The European Union in mid-October agreed to a reduction in customs checks and paperwork between the United Kingdom and Northern Ireland.
It involved special provisions for UK-only products — ending the so-called "sausage wars" that made headlines over the summer.
They refused, however, to scrap the European Court of Justice's oversight role concerned the Northern Ireland Protocol, as the British government had wanted.
What is Article 16 of the protocol?
Article 16 is a mechanism that allows either party to unilaterally take safeguard measures in the event that the protocol leads to "serious economic, societal or environmental difficulties that are liable to persist, or to diversion of trade".
It's unclear what the safeguard measures are considering London already unilaterally waived customs checks on some goods travelling from Great Britain to Northern Ireland. But they could see the UK suspend all its trade obligations under the protocol, say experts.
The measures are meant to be restricted in scope and duration to what is "strictly necessary in order to remedy the situation," the article says.
In other words, the measures are not meant to disrupt the functioning of the protocol or to suspend the protocol.
If either the EU or the UK triggers the clause, the other party may take proportionate measures to "remedy the imbalance".
The party that plans to carry out safeguard measures must notify the other party "without delay" and provide "all the relevant information". Both the UK and EU will then enter consultations to find a solution immediately.
Has Article 16 been triggered?
The EU previously came close to triggering Article 16 amid a row with pharmaceutical company AstraZeneca.
They considered triggering the article to impose export controls on COVID-19 vaccines coming from the European Union into Northern Ireland, amid worries that vaccines manufactured in the EU were being sent to the UK.
But the Commission quickly made a u-turn amid strong criticism from the Irish and British governments.
A July 2021 paper from the UK government on the protocol stated that "the circumstances exist to justify using Article 16" due to disruptions to trade in Northern Ireland.
The UK and EU have now entered into discussions to remedy the trade dispute.
Brexit minister David Frost told parliament in late October that "it is no secret that if we cannot reach agreement and we are still faced with a significant political problem in Northern Ireland, Article 16 exists".
What safeguarding measures can the UK take?
"It's not entirely clear what the UK government would do with Article 16 and what measures it would take," Jess Sargeant, a senior researcher at the Institute for Government think tank, told Euronews.
London has already unilaterally introduced grace periods on customs checks for certain goods and the Protocol states any measures need to address a specific issue.
"If the UK government says that problems are arising from the customs processes, they could claim that removing those processes by using Article 16 is removing the problem," Sargeant continued.
"But there is the suggestion that the UK government might actually go further and use Article 16 to try and suspend almost all of its obligations related to trade under the Protocol.
"It's not exactly clear whether that would be strictly within accordance of the terms of Article 16, or whether it would be acting outside of this. So we still don't know exactly what that would look like in practice."
What can the EU then do?
As per the Protocol, the triggering of Article 16 is immediately followed by a month of negotiations between the UK and the EU Joint Committee before any safeguarding measures are introduced. Once these are introduced, they must be reviewed every three months.
If Brussels however, decides that London is using Article 16 improperly or is in breach of the Withdrawal Agreement, it could turn to the dispute settlement mechanism.
"This would create an arbitration panel who would consider the issue and come up with a view as to whether the UK has breached the protocol and the [Brexit] Withdrawal Agreement more broadly," Sargeant said.
"If it found that it has breached it, then the EU could suspend parts of the Withdrawal Agreement and also the Trade and Cooperation Agreement," which would allow it to impose tariffs in some areas.
"That's quite a long process. It's likely it would take a number of years to get to the point of tariffs being introduced or cost retaliation through the Trade and Cooperation Agreement," Sargeant flagged.
The EU could however take some unilateral measures in the interim. This could include withdrawing the data adequacy granted to the UK which allows for personal data to flow between the two sides.
"There’s also a suggestion that it could just decide to suspend the Trade and Cooperation Agreement entirely," she said. This would take between nine and 12 months and result in significant barriers being introduced in areas including trade, law enforcement, judicial cooperation, aviation, road transport and energy amongst others.
What about Northern Ireland?
If the EU decides to go through the arbitration process and is found to be legitimate in its claim then it would be allowed to take retaliatory measures.
According to Sargeant, the obvious counterbalancing measures to a British decision to waive any sort of checks between Great Britain and Northern Ireland would be for the EU to impose checks between Northern Ireland and the Republic or between the Republic and the rest of the EU.
But the bloc is unlikely to proceed with such measures in a bid to preserve peace on the island of Ireland, Sargeant said.
"That's a good thing for Northern Ireland and stability, but at the same time, it perhaps gives the EU less leverage than they might have had otherwise," she said.
Instead, the EU would probably target Great Britain by ensuring it no longer benefit from the Trade and Cooperation Agreement.
But while it may seem like the UK has the upper hand given Brussels reluctance to impose any checks on the island of Ireland, triggering Article 16 would still "be particularly bad for Northern Ireland and lots of businesses are particularly worried that this could lead to more uncertainty, which could harm them even more," Sargeant said.
"There's also the question of the kind of political conflict it might create in Northern Ireland where this protocol has been a very kind of fractious issue," she warned.
"It's not clear whether part of this threat to trigger Article 16 is to try to gain leverage in the current discussions that are going on. If the EU believes that the UK is willing to trigger Article 16 then it might be willing to be more flexible or give a bit more in these negotiations on the protocol that are ongoing," she concluded.