Labour veteran Ken Livingstone has suggested that Labour MPs who voted in favour of airstrikes should be pushed out of their seats.
Mr Livingstone, who was controversially put in charge of the party's defence review, said if his MP had voted for airstrikes he would back a de-selection challenge.
Speaking on LBC, after 66 Labour MPs defied their leader Jeremy Corbyn to support military action in Syria, he said: "If I had an MP who had voted to bomb Syria then I would be prepared to support someone to challenge him."
Shadow foreign affairs minister Stephen Doughty said Mr Livingstone's comments were "utterly inappropriate" and told Sky News: "I really think Ken needs to consider what he is saying and think very carefully about his position."
Shadow work and pensions secretary Owen Smith said the comments were "disgraceful".
But speaking to Sky News later on Thursday, Mr Livingstone played down the comments and defended the right of MPs to vote with their conscience.
"Very few Labour MPs have every been de-selected," he said.
However, he added that if Labour party members decided to pre-select a different candidate, there should be nothing to stop them from doing so.
Mr Livingstone's sentiments could fuel the bullying and intimidation of Labour MPs who have supported the airstrikes or whose views are opposed to Mr Corbyn.
During the ten-and-a-half hour debate in the House of Commons on Wednesday, Walthamstow MP Stella Creasy was forced to leave the chamber to help staff at her office, who were under siege from protesters.
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Ms Creasy had been threatened with "de-selection" from the Labour party by supporters of Mr Corbyn, whose Momentum Labour group had called on Labour members to make their views on airstrikes in Syria known to MPs.
At the time, she had not even decided which way to vote.
When she did come out in favour of airstrikes after listening to Hilary Benn's speech, she was the target of vile abuse on social media.
A number of Labour MPs have been targeted with abusive messages and dubbed war criminals and traitors with blood on their hands.
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Mr Corbyn, who came to the leadership promising a new "kinder politics", was tackled over the hard Left abuse in the House of Commons by a number of MPs in his own party.
Labour grandee Alan Johnson took a swipe at the Labour leadership and said: "I find this decision as difficult as anyone to make.
"I wish I had the self-righteous certitude of our finger jabbing representatives of our new and kinder type of politics, who will no doubt soon be contacting those of us who support this motion tonight."
Later Mr Corbyn took to Twitter and Facebook to call for an end to the bullying.
He said: "I want to be very clear – there is no place in the Labour Party or from those that support us - for bullying of any sort, from any side of the debate.
"It flies in the face of everything I believe and everything I stand for."
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Deputy leader Tom Watson, who has also been the subject of trolling after voting in favour of the airstrikes, is to raise the need for a bullying and social media policy with Labour's ruling body, the National Executive Committee.
The Left Unity party, which was founded by film director Ken Loach, has posted the names of all the Labour MPs who voted with the Government encouraging Labour members to de-select them.
The deep and bitter divide in the party was compounded by shadow chancellor John McDonnell on Thursday morning when he compared Mr Benn's speech in the Commons to Tony Blair's pre-Iraq war address.
Mr McDonnell, who considers Mr Blair a war criminal because of his role taking the country to war in Iraq in 2003, said: "The greatest oratory can lead us to the greatest mistakes."
Mr Benn's speech was heralded as the greatest parliamentary oratory in a generation and received applause from both sides of the house.
But Mr Corbyn sat stony-faced and only grudgingly moved over to let Mr Benn take his seat again after delivering the speech.
Mr Livingstone has described Mr Benn's contribution as a "brilliant speech", but told Sky News that it lacked long-term vision.