The European Union shipped an ultimatum to Britain on Thursday, demanding it withdraw a proposal in advance of British lawmakers that would breach the Brexit divorce agreement the two sides signed late previous year.

The proposed legislation would give the British government power to override some of the most sensitive parts of the agreement that were aimed at averting the emergence of a challenging border amongst the British province of Northern Eire and Eire, an EU member. This was accomplished to avoid inflaming sectarian tensions on the island.