Dominic Raab resigned from Theresa May's cabinet this week over the draft Brexit deal, highlighting particular concerns with the measure aimed at avoiding a hard border in Ireland.
In an interview with the Sunday Times, he says the Taoiseach has behaved "irresponsibly" during negotiations.
He's also accusing the British Prime Minister of failing to stand up to 'bullies' in Brussels.
Meanwhile Theresa May's says the backstop measure aimed at avoiding a hard border in Ireland can only ever be temporary.
She's been defending the draft Brexit deal, which includes a provision to keep the North more closely aligned with the EU when it comes to goods and regulations.
Mrs May says both sides don't want to have to use it.