Union boss Len McCluskey has called on the Labour Party to adopt the full International Holocaust Remembrance Alliance (IHRA) definition of anti-Semitism.
Mr McCluskey, who is a close ally of Labour leader Jeremy Corbyn, said the party had been “insensitive” in not adopting the definition.
But the Unite general secretary, writing for HuffPost UK, prefaced his comments with a blistering attack on Jewish community leaders for what he called their “intransigent hostility” to Mr Corbyn.
Mr McCluskey said the problem of anti-Semitism in the party was “not manufactured” but had “certainly been wildly exaggerated”.
He said: “I am at a loss to understand the motives of the leadership of the Jewish community – the Board of Deputies, the Jewish Leadership Council and the Jewish Labour Movement.
“They raised entirely proper concerns, but have simply refused to take ‘yes’ for an answer.”
Mr McCluskey said the “more Corbyn has personally sought to build bridges” with the Jewish community, “the worse the rhetoric has become”.
He added: “What is the response from the leading Jewish community organisations to this record of reaching out, of understanding, and of action? Intransigent hostility and an utter refusal to engage in dialogue about building on what has been done and resolving outstanding difficulties.
“I therefore appeal to the leadership of the Jewish community to abandon their truculent hostility, engage in dialogue and dial down the rhetoric, before the political estrangement between them and the Labour Party becomes entrenched.”
Mr McCluskey, calling for the IHRA definition to be adopted, said: “Clearly, it would have been far better for the party to have adopted at least ten of the eleven IHRA examples in their original wording.
“Not doing so – and particularly without adequate consultation – was insensitive and bound to lead to misunderstanding, and also served to distract attention from the real issues at stake.
“It would be for the best if all eleven were now agreed, so the party can move on.”
But he warned there remained “free-speech problems” with the example concerning “Israel as a racist endeavour”.
He said: “That very example has been explicitly cited by pro-Israel campaigners, including Labour MPs, in urging the government to ban ‘Israeli apartheid’ events at colleges.
“The House of Commons Home Affairs Committee expressed free speech concerns about it too.”
Mr McCluskey went on to warn against the party descending “into a vortex of McCarthyism” in a bid to root out anti-Semites.
The Unite leader used his blog to accuse certain Labour MPs of using the row over anti-Semitism as a method to “provide rocket fuel for a split in the Party”.
He said: “Let those few Labour MPs looking to break away from the Party do so on an honest basis, embracing capitalism, the free market and the alliance with Trump’s America, and not pretend that Labour is something it is not, an institutionally racist party.”
In response to the blog the Board of Deputies, which is the main representative body of British Jews, said: “We note that Len McCluskey has advocated the adoption of the full IHRA definition of anti-Semitism and its illustrative examples.
“However, his attack on the Jewish community is both unfair and unwarranted.”
The spokesman added: “We have had a deluge of words from the Labour leadership.
“It is about time that the party resolved this crisis by taking the firm and decisive action which the communal leadership set out for them in detail months ago.
“They have so far failed to do what is right.”