The EU is expected to launch legal action against the UK government on Wednesday over its decision to scrap some post-Brexit trade arrangements.
Ministers insist current checks on some goods travelling from Great Britain to Northern Ireland must end to avoid harm to the peace process.
They published a parliamentary bill on Monday aimed at overriding parts of the deal signed with the EU in 2020.
But Brussels says going back on the arrangement breaks international law.
The Northern Ireland Protocol is the part of the Brexit deal which keeps Northern Ireland in the EU’s single market for goods.
This prevents a hard border with the Republic of Ireland – including checks there on the movement of people and goods – which both the UK and EU want to avoid in order to ensure peace is maintained.
But instead it means checks on some goods arriving into Northern Ireland from other parts of the UK. That is opposed by unionists in Northern Ireland who argue it creates a trade border in the Irish Sea and could lead to the break-up of the UK.