Owen Smith has been sacked as British Labour Party spokesman on Northern Ireland after breaking ranks with leader Jeremy Corbyn by calling for a new European Union referendum.
He was dismissed from the shadow cabinet after saying that Labour should keep asking whether Brexit remains the right choice for the UK.
Mr Smith said he had been sacked for his views on the "damage" Brexit will do to the UK's economy and the Good Friday Agreement.
In an apparent message to Mr Corbyn he added: "Those views are shared by Labour members and supporters and I will continue to speak up for them, and in the interest of our country."
Mr Smith, who unsuccessfully challenged Mr Corbyn for the party leadership in 2016, insisted Labour needed to do more than "just back a soft Brexit."
Mr Corbyn has been careful to say that Labour is not seeking a referendum on a Brexit deal, but has avoided completely ruling out such a vote.
In a sign of the leader's anger at Mr Smith's intervention, he was asked to stand down from the frontbench and replaced with immediate effect by former minister Tony Lloyd.
Mr Corbyn said: "Tony is a highly experienced former government minister who is committed to ensuring that peace in Northern Ireland is maintained and helping to steer the devolution deal back on track."
Mr Lloyd said: "As we leave the European Union, ensuring there is no hard border between Northern Ireland and the Republic is of paramount importance and this will be my number one priority.
"This is an incredibly important job, with a huge in-tray and I am looking forward to starting work."