Jeremy Corbyn is facing a backlash over his so-called revenge reshuffle after a wave of senior figures spoke out in support of the first casualty.
Michael Dugher announced he had been "sacked" from the post of shadow culture secretary as part of the Labour leader's shake-up of the shadow Cabinet.
But Mr Corbyn's decision to kick out the Barnsley East MP, a close ally of former prime minister Gordon Brown, saw MPs express their dismay at the move.
And the party said a planned meeting of the shadow cabinet which had been set for 12.45pm had been cancelled.
Labour deputy leader Tom Watson led the praise for the ousted frontbencher.
He said: "Michael Dugher is a rare politician - a talented working-class MP who hasn't lost his strong Yorkshire roots.
"Politicians with his ability and commitment can make a difference in any role. Labour's loss in the shadow cabinet will be compensated by Michael's free thought on the backbenches."
Gloria De Piero, shadow minister for young people, said: "In over 20 years of friendship with Michael I have witnessed his tireless commitment and determination to campaign for a Labour government and I know that will continue from the back benches. But it's always sad to lose someone from an ordinary background from the shadow cabinet."
Luciana Berger, shadow minister for mental health, said: "Sorry @MichaelDugher leaving the shadow cabinet. One of @UKLabour's best campaigners who's worked hard to widen access to the arts & sport."
Shadow Northern Ireland secretary Vernon Coaker wrote: "Really sorry to see @MichaelDugher leave Shad Cab. He will be missed! He will be just as ferocious attacking the Tories from the b/benches."
Fellow Barnsley MP Dan Jarvis, who is widely tipped as a future party leader, said: "Sad to see this. @MichaelDugher is a highly effective & authentic voice 4 working ppl & a great champion for #Labour."
Former leadership contender Andy Burnham said Mr Dugher, who ran his campaign, had served the party with distinction.
He said: "We face a big challenge in winning back the trust of our traditional supporters in the North and the Midlands and Michael is one of the authentic voices who can do that. I thank him for all the support he has given me and wish him well.
"He has served Labour with distinction and can leave the front bench with his head held high."
Shadow defence minister Toby Perkins said: "Sad to hear this, always effective at putting Tories on the back foot, something we need to do more of."
Jon Ashworth, shadow minister without portfolio, said: "I've been mates with @MichaelDugher since I was 16. Sorry to hear this news. I know he will continue to campaign hard for the party he loves."
Graham Jones, Labour MP for Haslingden and Hyndburn in Lancashire, tweeted: "With the sacking of Dugher, traditional working-class Labour is dying."
But Bassetlaw MP John Mann tweeted: "All this guff about @MichaelDugher. He's a mate of mine. But Corbyn won. It's politics. Personally I wouldn't have freed him up, but then.."
Mr Dugher voted in favour of UK military action in Syria in last month's free vote in the House of Commons. He had warned Mr Corbyn he would end up with a "politburo of seven" at the top of the party if he attempted to use a reshuffle to surround himself with allies from the Labour left.
In a message on Twitter, Mr Dugher announced: "Just been sacked by Jeremy Corbyn. I wished him a happy new year."
Mr Corbyn is expected to use the first day of the Commons' return from Christmas recess to finalise the shake-up of his top team, after late-night talks with key members of the shadow cabinet ended without any announcement on Monday.
A spokesman for Mr Corbyn said the leader had "several discussions in relation to changes to the shadow cabinet" but would not give any details of who, if anyone, was being moved or sacked.
The talks followed speculation of a possible "purge" of those with views at odds with the leader, including shadow defence secretary Maria Eagle's support for the renewal of the UK's Trident nuclear deterrent.
Another nine shadow cabinet members voted for air strikes after Mr Corbyn was forced to allow a free vote - fuelling suggestions that he could replace them with left-wing supporters.
But the scope of the changes appeared increasingly likely to end up narrower than mooted, as the leadership sought to balance the desire for a coherent message on the front bench with the major backlash in the parliamentary party that would greet any move to freeze out moderates.