The UK government has been left angered after the EU published a technical note calling for more post-Brexit detail on the Northern Irish border without discussing with London first.
The note from the European Commission warns that key preparations for the Northern Ireland Protocol must be under way by July 1 if it is to come into effect at the end of the Brexit transition period.
The protocol argues that there will not be a border on the island of Ireland, but preparations must be in place to allow for customs checks and regulatory checks between Britain and Northern Ireland.
In the note circulated to member states the EU says it is the biggest challenge facing the implementation of the Withdrawal Agreement.
It warns that there is a whole host of requirements that need to be satisfied in the coming weeks, and IT systems and customs databases need to be started in the next four weeks.