But what is the protocol? And why has it caused so much anger in Northern Ireland among Unionists?

With an announcement on the agreement due later this week, here’s all you need to know.

READ MORE: EU needs to recognise Northern Ireland Protocol has 'failed', say DUP

What is the Northern Ireland Protocol?

As part of the EU Withdrawal Agreement, the Northern Ireland Protocol helps prevent any checks on goods along the land border between Northern Ireland and the Republic of Ireland.

Both sides agreed during Brexit negotiations that protecting the 1998 Good Friday Agreement was a priority. This meant keeping the land border open, and instead created a trade border along the Irish Sea instead.

When Northern Ireland and Ireland were both in the EU this was simple as the rules on trade were the same and no goods checks were needed travelling between countries.

However, after Northern Ireland left the EU along with the rest of the UK, a new arrangement was needed as the EU requires many goods to be inspected when they arrive from non-EU countries, such as milk and eggs. Some products are not allowed to enter at all.

When was it brought in?

The protocol came into force on 1 January 2021 and is now part of international law. However, there were a number of ‘grace periods’ to allow checks to be brought in on a phased basis.

One of those periods ended on July 1, but as both sides could not reach an agreement on how to proceed, it has been extended while negotiations are ongoing.

READ MORE: Who is Maros Sefcovic? Inside look at EU's Brexit negotiator

How do goods checks between Great Britain and Northern Ireland work?

Northern Ireland is still in the EU single market for goods, with EU custom rules enforced at its ports.

This means that to avoid good checks along the Irish land border, it was agreed that some checks would be undertaken at ports in Northern Ireland from products coming from England, Scotland or Wales.

Customs documents have to be filled in, and it has prompted criticism that a border has effectively been created in the Irish Sea instead.

What is Article 16?

The mechanism, created as a temporary measure, is supposed to be a last resort. The article is intended to be used when the protocol is leading to serious “economic, societal or environmental difficulties”.

Both the UK and EU can act unilaterally, without needing the agreement of the other side, under the article without the protocol being suspended.

The idea is that it can be used when the two sides can’t agree on a solution.

READ MORE: Northern Ireland Protocol 'isn't sustainable' Brexit minister says

Will either side trigger it?

Potentially. Brexit Minister Lord Frost told parliament’s European Scrutiny Committee this week that “all options” were on the table, including triggering Article 16.

The DUP have urged the UK Government to use it.

The EU previously used Article 16 in January amid a row over vaccine supplies, but quickly back tracked.

What has Boris Johnson said about the protocol?

The Prime Minister has attacked the EU on multiple occasions over the implementation of the protocol.

On July 7 he said their application of the protocol was “grossly disproportionate and unnecessary”.

During the committee session, he told MPs that the protocol didn’t pose any threat to Northern Ireland’s status in the UK.

READ MORE: DUP sets out seven tests for Northern Ireland Protocol

Why are Unionists in Northern Ireland upset at the protocol?

Unionists strongly oppose the additional checks on goods arriving into Northern Ireland from the rest of the UK, arguing it undermines the Union.

The DUP have laid out seven promises they want the UK Government to keep in mind while negotiations are ongoing as they say the current arrangements mean that those in Northern Ireland are now not entitled to the same privileges as those living in the rest of the UK.

There have been protests in Northern Ireland over the protocol, with unionists arguing it makes the Good Friday Agreement void.

Due to the creation of the border in the Irish Sea, Unionists feel as if they have been cut off from the rest of the UK and see it as an attack on their British identity. This anger was seen as a contributing factor when rioting erupted in some parts of Northern Ireland in April.

DUP leader Donaldson has called on the UK to renegotiate the protocol

What is the Republican view?

Sinn Fein (SF) said the protocol is “the answer, not the problem” and warned any unilateral action from the UK would not be acceptable.

SF president Mary Lou McDonald has said that the protocol is needed to “protect the infrastructure” of the Good Friday Agreement.

She said any assertion that the protocol will be abolished are “fanciful” and that issues that arise should be addressed by the joint EU-UK committee.

READ MORE: Boris Johnson attacks EU again over NI Protocol

What should we expect to happen next?

Brexit Minister Lord Frost told MPs during a committee session that he will make a statement on the UK’s current position later this week, possibly Wednesday (21 July).

EU Commission Vice President Maros Sefcovic met with DUP leader Sir Jeffrey Donaldson at the beginning of this week, and is said to have been meeting with many others in Northern Ireland to get a wide range of views. Donaldson called on the UK to renegotiate the agreement and said it had "failed". 

Whether either side will trigger Article 16 if they cannot reach an agreement is yet to be seen.