Brexit could mean a “dangerously high cost” for peace in Northern Ireland, a former minister has warned.
Ex-Labour Northern Ireland Secretary Lord Hain said the peace process could “so easily unravel”.
He said the Brexit bill should be changed to support maintaining the open border between Northern Ireland and the Republic of Ireland.
But former Northern Ireland First Minister Lord Trimble said this was unnecessary.
They were speaking as peers debated the government’s draft legislation that will authorise the UK’s departure from the EU.
Among several amendments that have been proposed is Lord Hain’s, which would require the prime minister to support the maintenance of the open border between Northern Ireland and the Republic of Ireland as set out in the Good Friday Agreement.
He said: “If the referendum means Brexit at any price it may well mean a dangerously high cost for the Northern Ireland peace process.”
Prime Minister Theresa May has previously said there will be no return to the “borders of the past” after Brexit and that she wants to see “seamless movement” between Northern Ireland and the Republic.
Lord Trimble said the PM’s stance meant it was “unnecessary” for the bill to be amended.
Other proposed amendments which will be considered by peers focus on the rights of EU nationals living in the UK to remain after Brexit, and calls by Labour for a “meaningful vote” on the deal reached after the negotiations.
MPs have already voted in favour of the government’s Brexit bill, which was drawn up after the Supreme Court ruled that Mrs May could not invoke Article 50 of the Lisbon Treaty without consulting Parliament.
If the Lords back any amendments to the legislation, it will return to the Commons where MPs will decide whether to accept peers’ proposals.