Jeremy Corbyn has been warned that he needs to do more to tackle anti-Semitism or risk splitting Labour’s main Jewish group away from the party.
Members of the Jewish Labour Movement (JLM) agreed in an indicative vote to remain affiliated with the party, maintaining a link stretching back almost 100 years.
But the party’s leadership was given a month to act on the group’s concerns.
And in a sign of how bitter the divide has become, Labour MPs who failed to sign a pledge of solidarity with the group were accused of “moral cowardice” by one of their parliamentary colleagues, while another likened the problem to “fascism”.
Hundreds of JLM members gathered at a synagogue in central London, with another meeting taking place in Manchester.
JLM national secretary Peter Mason said members had backed retaining their affiliation with Labour, which dates back to 1920.
“We had an indicative vote this evening that we will stay, we will stand and we will fight against anti-Semitism in the Labour Party,” he said.
“The message from the Jewish Labour Movement this evening was absolutely clear.
“If the Labour Party fails to show solidarity to us, we will not show solidarity to it.
“That counts for MPs who do not sign their names to letters showing solidarity with us, that counts for members of the Scottish Parliament, that counts for councillors.”
He added: “It is very clear: we have set the tests that the leadership need to meet and we expect them to do that before our AGM on April 7.”
Labour MP Wes Streeting said it had been a “painful” meeting and warned the party was “on notice” to address concerns.
He hit out at colleagues for failing to sign up to a letter organised by fellow MP Stella Creasy expressing solidarity with Jewish members.
“I’m relieved that people are committed to staying and fighting but it is very clear, listening to what our Jewish colleagues and comrades and friends are saying, that we are so far away as a political party from having the trust and confidence of the Jewish community,” he told the Press Association.
“This is ultimately about leadership and Jeremy Corbyn has to decide whether he is going to be a leader who repairs and strengthens or whether he is going to go down in history as the Labour leader who broke the Labour Party.”
Mr Streeting added: “More than 100 Labour MPs signed a letter of solidarity with the Jewish Labour Movement. But where was the majority of my parliamentary colleagues and why are they showing such moral cowardice in the face of such pain from our Jewish members?
“They have a responsibility to step up as well.”
The JLM said it had made a submission to the Equalities and Human Rights Commission in November last year, asking it to investigate the allegation that the Labour Party was institutionally anti-Semitic.
A spokesman said: “We did not take that decision lightly… This evening Jewish Labour members made clear that we will not unconditionally stand by whilst we are treated with such intolerance and contempt.
“We, in our history, have loved and respected the Labour Party too much to let this continue.”
Dame Margaret Hodge said it was an “emotional and angry but determined” meeting.
“I fought fascism on the right when I defeated the BNP, I will now fight fascism on the left,” the Barking and Dagenham MP said.
Dame Margaret said the scale of the problem makes it “utterly incredible to me that only 12 people have been expelled”.
“If there is zero tolerance of anti-Semitism, you have got to show that in your actions.”
The Labour leader defended the party’s handling of anti-Semitism cases following accusations by Dame Margaret that members of his team interfered to reduce the sanctions that were imposed.
On Tuesday, Dame Margaret claimed that Mr Corbyn had either misled her or been misled himself about the extent of his team’s involvement in such cases.
In a letter to the MP, Mr Corbyn acknowledged that a “very small group of staff” in his office were asked by the party’s governance and legal unit (GLU) to help clear the backlog of cases that had built up.
Mr Corbyn said the help provided by staff from the Leader of the Opposition’s Office (Loto) had been during the transition from former general secretary Iain McNicol to his successor Jennie Formby.