Boris Johnson agreed the Northern Ireland Protocol with the European Union in October 2019 but his government has spent the past 18 months trying to change it.
After hundreds of hours of talks, the UK government claims it is being forced to act unilaterally to amend the protocol because the EU is refusing to address the core problems with the agreement.
Foreign Secretary Liz Truss said the Norther Ireland Protocol Bill, which has been tabled in the Commons "will uphold the Belfast (Good Friday) Agreement and support political stability in Northern Ireland".
But a majority of Northern Ireland's lawmakers have written to Mr Johnson saying they reject his plan to override the protocol, in the "strongest possible terms".
And the European Union says amending aspects of the agreement would amount to the UK breaching international war and is threatening a trade war in an attempt to keep the protocol in place.
So, what is the Northern Ireland Protocol?
The Northern Ireland Protocol is a major aspect of the Brexit Withdrawal Agreement which Mr Johnson agreed with the EU, after taking over from Theresa May as prime minister.
A bespoke arrangement around NI needed to be found because it shares a land border with the EU, through Ireland, and the precarious political situation there, stabilised by the Good Friday Agreement, means politicians want to avoid a hard border on the island of Ireland at all costs.
So lawmakers were faced with a problem; protecting the EU's single market from UK goods which may not comply with European standards while allowing trade to flow freely on the island of Ireland and ensuring trade could continue unfettered between NI and Great Britain.
The Northern Ireland Protocol was the solution negotiated by both sides and agreed by Mr Johnson in October 2019.
The protocol prevents a hard border between NI and Ireland, which would involve checks on goods and services moving south, by placing some checks on trade flowing to NI from Great Britain.
Fans of the protocol say it gives Northern Ireland the best of both worlds, access to the EU's single market while remaining part of the UK.
What problems is it causing?
Critics say the checks on products coming from Great Britain to Northern Ireland effectively cut it off from the rest of the UK and they are seriously affecting trade.
The Democratic Unionist Party in Northern Ireland feel so strongly about problems being caused by the protocol that they are refusing to enter a power-sharing government with rivals Sinn Fein until the issues are resolved.
Northern Irish businesses which bought products from the rest of the UK are being so severely impacted by the bureaucratic checks - which the government insists are unnecessary - that many have been forced to stop trading.
The government is unhappy with the aspect of the protocol which says goods need to comply with EU rules in order to be placed on the Northern Ireland market even when they will never enter the EU single market.
This is causing issues for businesses because they are being forced to complete new paperwork and processes, or comply with specific product requirements not relevant to them.
The UK government also takes issue with the tax rules baked into the protocol which it says is preventing Northern Ireland from being able to take advantage of changes in the rest of the UK, such as VAT cuts.
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Under the protocol, Northern Ireland is still subject to EU state aid rules which ensures open and fair competition among nations in the bloc.
This, the government says, limits the level of support available in Northern Ireland compared to the rest of the UK.
This kind of support cannot be granted without EU approval, "creating significant uncertainty and a two-tiered system in the UK", according to the government.
Any dispute between the UK and EU regarding Northern Ireland is adjudicated by the European Court of Justice, something the British government says damages the sovereignty many Brexit-backers voted for.
And the DUP also says the protocol is risking political stability because it impacts an aspect of the Good Friday Agreement which says Northern Ireland should remain an equal part of the UK unless a majority agreed otherwise.
Another part of the Good Friday Agreement says Northern Ireland should be governed by a power-sharing executive, which the DUP is refusing to enter over in protest over the protocol.
Prime Minister Johnson says it is essential that issues with the protocol are resolved in order to restore a government in Northern Ireland so it can tackle the cost-of-living crisis.