The Tánaiste claims the Good Friday Agreement has been "shaken" by the British Prime Minister's 'aggressive' approach to Brexit.
Simon Coveney says the whole point of the 1998 deal was to unite communities and eliminate borders.
But he says Boris Johnson wants Brexit to create 'divergence' between Britain and EU.
The Tánaiste says that's bad news for stability in Northern Ireland.
"That delicate balance that was responded to by a Good Friday Agreement which has done incredible things for this island is now certainly shaken by Brexit and the new and more aggressive approach to delivering Brexit that this prime minister has brought," Mr Coveney said.