The EU has pledged to use all measures at its disposal in response to the government bill that would unilaterally override parts of the Northern Ireland protocol, a step that Brussels and many Conservative backbenchers see as a flagrant breach of international law.
While the threat of an economically-damaging trade war has captured the headlines, it will not be the first move of the EU.
The EU is likely to trigger new legal complaints over the government's failure to implement parts of the Northern Ireland protocol later in the day. Northern Ireland remains in the EU's single market for goods and the European court of justice has jurisdiction.
Last March, Brussels started a legal action against the government after the government announced that supermarkets and their suppliers would not have to comply with EU food rules, a unilateral extension of a grace period. The EU suspended its legal action in July as a goodwill gesture to help restart talks, but it is now likely to revive this case, which could end with the ECJ imposing daily fines.
The European Commission has a lot of gripes about the British implementation of the protocol, including a unilateral decision to waive some checks on cold meats and the failure to provide data and build border inspection posts. The complaints of the UK could end up in the ECJ.
As one of the expected clauses in the bill is the removal of ECJ jurisdiction, this legal action is one of the weaker weapons in the EU's arsenal.
British participation in EU's research programme Horizon : €96 bn 81 bn Is there a memo on financial services to create a talking shop on regulation? The mooted agreements will remain in the deep freeze for the duration of the dispute over the Northern Ireland protocol. The ambassador to London of the EU, Jo o Vale de Almeida, regrets that researchers were collateral damage in the protocol dispute. Any positive agenda will remain stalled, as London and Brussels will cooperate on sanctions against Russia.
Individual member states may also choose to put pressure on the government, for example, France could step up checks on British goods entering the EU. More onerous checks will mean more lorry queues at Dover.
The EU and the UK have agreed to impose tariffs on British goods, or even suspending the entire trade and cooperation agreement. When the EU got into a trade war with Donald Trump's White House, it imposed tariffs on Harley Davidson motorcycles, jeans and bourbon. It is expected that in the event of a trade war with the UK, Brussels would target iconic British goods.
It's not a quick fix to impose tariffs. The EU must go through the exact dispute settlement process outlined in the Brexit withdrawal agreement. The case would go to a ministerial joint committee led by the foreign secretary, Liz Truss, and the European Commission vice president Maro ef ovi. The next step would be an independent arbitration panel that can impose fines on the guilty party. The trade deal between the EU and the UK can only be suspended in the event of persistent rule-breaking. The EU governments, which are grappling with the soaring cost of living, hope to avoid what they see as a pointless, costly row.
As tensions rise, the EU will offer talks on existing proposals to ease customs checks at the Great Britain Northern Ireland border. This is a general approach throughout the process of leaving, which is not wanting to be the party that pulls the plug on negotiations.
The threat has triggered the opposite response: the EU has united in defence of the protocol and British negotiators hope that the bill will force compromises.