Attacks on the Stop the War coalition by a former shadow cabinet member have been described as "unjustified".
Tristram Hunt said it was a "disreputable" organisation as he appealed to Labour leader Jeremy Corbyn not to attend a fundraising event for the group in London later this week.
Despite the call, Mr Corbyn has made clear he will go ahead with an appearance at the event for the coalition, which he used to chair prior to his election as party leader in September.
Mr Hunt told BBC1's Andrew Marr Show yesterday: "The Stop the War coalition picketed the Labour Party headquarters when we were trying to run a phone-bank for the Oldham by-election so they were preventing the election of a Labour Member of Parliament.
"We have also seen some pretty ugly comments from them about Hilary Benn and the fact that Hilary Benn should be sacked. Also their comments about Islamic State, their comments about how the French almost had it coming to them.
"They are a really disreputable organisation."
A Stop the War statement said: "Tristram Hunt's attack is unfounded and unjustified. We did not picket Labour Party offices, we have unequivocally condemned the terrible massacre in Paris, and we do not take a view on who should hold which office in the Labour Party.
"We do note, however, that unlike Mr Hunt we take the same view of the Syrian War as the leader of the Labour Party and the great majority of Labour MPs and members. We look forward to celebrating that fact with Jeremy this week.
"Mr Hunt has been wrong about all the wars Britain has fought this century. He is entitled to his errors, but Stop the War and others are entitled to peacefully protest against them, and we shall continue to do so."