Jeremy Corbyn has sacked a shadow cabinet minister who broke ranks with official Labour Party policy to call for another EU referendum.
Owen Smith was asked to stand down as shadow Northern Ireland secretary by the Labour leader, after demanding a second vote after EU talks have ended.
He has been replaced by Rochdale MP and shadow housing minister Tony Lloyd.
Mr Smith said he would continue to "speak up" for what he called his "long-held views" on Brexit.
He said in a tweet that his concerns about Brexit, which he outlined in a Guardian article, were shared by other supporters and members of the Labour party.
Just been sacked by @jeremycorbyn for my long held views on the damage #Brexit will do to the Good Friday Agreement & the economy of the entire U.K. Those views are shared by Labour members & supporters and I will continue to speak up for them, and in the interest of our country.— Owen Smith (@OwenSmith_MP) March 23, 2018
Shadow home secretary Diane Abbott said Mr Smith could not sit on Labour's frontbench while advancing a position against party policy.
Ms Abbott, who in November told constituents she would push for a referendum on the final Brexit deal - before clarifying she wanted a Parliamentary vote - said Mr Smith would be able to "make a contribution to the debate" outside the shadow cabinet.
By Jonathan Blake, BBC political correspondent
In a phone call from Jeremy Corbyn and what a source described as a "civil conversation", Owen Smith was told he was being sacked.
Mr Smith's comments on Brexit policy were seemingly a step too far for the party leadership, who'd welcomed him back into the fold after his leadership challenge in 2016.
The angry response from some MPs has again laid bare their opposition to Jeremy Corbyn as leader.
But Mr Corbyn's grip on power in the party has never been stronger.
The fact that he can make this move without fear of open rebellion, is a demonstration of that.
Labour peer Lord Hain, a former Northern Ireland secretary, called the sacking a "Stalinist purge" - and said Mr Smith was widely respected for his work on Northern Ireland.
Labour MP Chuka Umunna said it was "extraordinary" that Mr Smith had been sacked for advocating a Brexit policy which he said had wide support in the party.
Fellow MP Anna Turley said Mr Smith's departure was "disappointing" and he would be a loss to the front bench, while former cabinet minister Ben Bradshaw told Mr Smith he was "very sorry" to see him go.
Mr Corbyn said his replacement, shadow minister for housing, communities and local government Mr Lloyd, was "highly experienced".
He said Mr Lloyd was "committed to ensuring that peace in Northern Ireland is maintained", as well as helping to steer the devolution deal "back on track".
In the article, Mr Smith called for Labour to back membership of the EU single market.
The Labour leader announced last month that the party wanted the UK to be a permanent member of a customs union with the EU after Brexit.
But 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 or guarantee a soft border in Ireland".
Its extraordinary that a shadow cabinet member -doing an excellent job in their brief - should be sacked for standing up for our principles and advocating a Brexit policy that commands the overwhelming support of our members, supporters and voters. What has happened to our party? https://t.co/DBYDlNXSZ0— Chuka Umunna (@ChukaUmunna) March 23, 2018
He wrote: "If we insist on leaving the EU then there is realistically only one way to honour our obligations under the Good Friday Agreement and that is to remain members of both the customs union and the single market."
Labour's shadow Brexit Secretary Sir Keir Starmer has said the party was "not calling for a referendum at this stage".