(Reuters) – David Frost, British Brexit Minister, called on Tuesday in Lisbon for “significant changes” in the European Union’s post-Brexit trade rules with Northern Ireland.

The EU was due to present its proposal for resolving a disagreement over the Brexit deal.

This is a brief explanation of the issues at stake when talks take place between Britain and EU over the Northern Ireland Protocol.

THE PROTOCOL – Both the EU and Britain agreed that keeping the Northern Ireland/Ireland border open was essential to preserving the 1998 peace deal that ended three decades of sectarian violence, but argued over how to do this after Brexit.

A protocol established a special arrangement that allowed British-ruled Northern Ireland to join the EU single trade market for goods. This means it is bound by the EU rules in this region, especially for animal products like meat and milk.

In order to stop certain goods coming into Northern Ireland via mainland Britain without proper paperwork or checks, such goods must be documented and checked.

After four years, the Northern Irish Assembly may vote on whether or not to keep the protocol. A simple majority voting against would mean that the protocol will be removed after two more years.

PROBLEMS – Pro-British unionists say the protocol undermines peace by dividing them from the rest of the UK with an effective border in the Irish Sea. This discontent was responsible for the worst violence of the past few years in the area in March and April. However, there have been very few such conflicts since.

London speaks out about practical issues, pointing out that Northern Ireland has been severely affected by certain products due to the obstacles. Last month, the EU granted British extensions of grace periods to defer some more difficult checks.

Britain complained also that the protocol led to trade diversion. According to Irish statistics, Irish exports rose by 45% in the first seven month of this year. Imports into Ireland increased by 60%. Comparable data for British/Northern Irish trade has not been released.

EU, UK PROPOSALS: Britain demanded that in July the EU revise the protocol so that it only applies to goods intended for the EU. It also required that UK regulations and EU rules co-exist in Northern Ireland. The agreement was also rewritten to remove the oversight by EU judges.

On Wednesday, the European Commission will present to Britain a set of measures that ease customs control, the clearance of food and medicines, and facilitate the movement of medicine to British provinces from the UK mainland. But it won’t provide London with the comprehensive overhaul they want.

EUROPEAN COURT of JUSTICE – The EU repeatedly denied Britain’s request to have the Protocol supervised by the European Court of Justice, (ECJ). This is still a significant point of contention.

EU stated that it does not see how an EU body, other than its top court, could decide on EU market issues. According to the European Commission’s chief official in charge of the matter, nearly no one brought up the ECJ during a recent visit to Northern Ireland.

Frost stated that Frost’s comments about the ECJ’s involvement in protocol operation have created a profound imbalance and that the Commission was too quick to ignore governance.

Article 16 – Frost once again suggested that Britain could trigger Article 16 to effect changes. But he in Lisbon said it wouldn’t “go down this road gratuitously nor with any particular pleasure.”

Article allows the EU to unilaterally take “safeguard” measures against Britain or the EU if it causes serious economic, social, or environmental problems.

This Article 16, which is described as an emergency brake says that any measure should be limited in scope and duration and only used to solve problems.

This initiates a dialogue to resolve the specific issues. They would meet immediately and then the safeguard measures won’t come into force for one month. The talks would go on for three more months in order to reach a resolution.

“Proportionate rebalancing” can be used to retaliate against any side that believes their interests have been compromised by safeguard actions. Article 16 is still in effect.