A Church of Ireland bishop sent an open letter to the British Prime Minister warning of the "incalculable consequences" of no-deal Brexit because of fears such a move would undermine the Good Friday Agreement.
Bishop of Clogher Rt Rev John McDowell wrote to Boris Johnson in July after he was appointed Prime Minister following the resignation of Theresa May.
In it, he said no government should "commit a country to a course of action in which the consequences were so opaque as to be incalculable."
Rev McDowell also expressed concern that Brexit was re-awakening concerns over the border.
"The ground on which people build and grow in the border region feels particularly fragile today," he wrote.
"It is almost possible to feel the heat of the past burning the soles of our feet. So please, in your consideration of the future of this place: tread carefully.
"And with deep and genuine concern I ask you to be very conscious of the legacy your government will leave."
The Bishop, whose diocese includes six border counties, today said he was concerned that a no-deal Brexit could undermine the Good Friday Agreement.
"We should not underestimate the magnitude of what was achieved in 1998 and let that slip through our fingers," he told BBC Radio Ulster's Sunday Sequence programme.
He said he border question had "a bit like the gun in 1998" been largely taken out of Irish politics by the agreement.
"What my concern was that it was being brought back in, right into the centre of politics and there seemed to be in certain quarters a lack of of understanding about what that might unearth," he explained.
"Things have a habit of escalating and we don't know what they will escalate to.
"As I said in the letter, the lava isn’t far below the surface in Ireland and Irish history and some times it doesn’t take much to break through the crust if it’s clumsily handled."
As a former assistant director of the Confederation of British Industry (CBI) in Northern Ireland, the Bishop said he had been motivated to write the letter after a civil service report warned of the potential loss of 40,000 jobs in a no-deal Brexit.
He was asked if he was possibly out of step with his flock as both unionist parties, the DUP and Ulster Unionists are in favour of Brexit.
"To be frank, sometimes its not my job to be in step with my flock, " he replied.
"My job is to some degree to lead and to sometimes say things out of a conscientious concern because I think it’s something that’s the right thing to say and that I should be saying provided i can say it reasonably and calmly and can defend it."
The Bishop said the prime minister had not replied to his letter, but he had not expected him to do so.