The Board of Deputies of British Jews has formally declared the Green Party of England and Wales a racist organization following its adoption of a resolution equating Zionism with racism.
The decision, approved by an overwhelming majority of 118 votes to one, came in response to a policy motion passed at the Greens' annual conference earlier this month.
Phil Rosenberg, president of the Board of Deputies, Britain's largest Jewish representative organization, said the party had crossed a fundamental line by adopting a position that characterized a central component of Jewish identity as racist.
"By adopting an antisemitic platform, the Green Party of England and Wales has become a racist party. We will treat it accordingly," he said as quoted by the BBC.
"No political party has the right to tell Jews that a central part of our identity, rooted in thousands of years of history, faith and peoplehood, is racist."
"The Green Party's policy brands much of our community, including our synagogues and communal organisations, with that slur. It gives prejudice against Jews a political licence. The Green Party's leadership must now take responsibility for reversing this policy and confronting the antisemitism it has legitimized," said Rosenberg.
The Board of Deputies also called on other political parties to refrain from entering coalition agreements or other political arrangements with the Greens unless the controversial policy is repudiated.
According to the resolution, parties cooperating with the Greens at either the local or national level would be "failing to take antisemitism with the requisite seriousness" unless the relevant Green leadership had explicitly rejected the motion and committed to overturning it.
The dispute centers on a resolution adopted by Green Party members earlier this month that defines Zionism as an ideology advocating "an ethnonationalist Jewish state in historic Palestine to the exclusion and/ or domination of the non-Jewish population".
The motion immediately generated criticism from Jewish organizations, opposition parties, four Green members of Parliament, and two former party leaders.
Prime Minister Andy Burnham, who has himself faced controversy over his positions on Israel, condemned the resolution as "completely wrong" and an example of "terrible judgement".
Burnham subsequently announced that his Labour Party would not cooperate politically with the Greens while the policy remained in effect.
The Green Party rejected the Board of Deputies' latest condemnation.
A party spokesman insisted that the Greens do not discriminate against individuals who identify as Zionists and rejected the Jewish organization's "characterization of this motion and our party".
The spokesman added that the decision "will not stop us from speaking out against the genocide in Gaza and pushing for stronger sanctions against the Israeli government and its leaders".
Green Party leader Zack Polanski, who is Jewish, did not participate in the conference vote because he had departed early to campaign in the Holborn and St Pancras parliamentary by-election, which took place several days later.
In a subsequent BBC interview, Polanski acknowledged that he wanted changes to the resolution but said he would not seek to repeal it. Under the party's rules, the policy is expected to remain in place until 2028.
Polanski also faced scrutiny during a separate interview on BBC Radio 4, when he repeatedly declined to answer directly whether Israel has a right to exist.
Presenter Nick Robinson pressed the Green leader on the question, but Polanski instead criticized Israel's treatment of Palestinian Arabs and accused the country of apartheid and genocide.
"I don't believe any state has the right to oppress or to commit apartheid and certainly not genocide on another people," Polanski said, adding, "I don't believe that's a state that anyone should be supporting."
Robinson then asked Polanski to provide a clear "yes/no" response to the question of Israel's right to exist.
Polanski again declined to give a direct answer.
"I've repeated many times that I want to see equal rights for Israelis and Palestinians - at the moment Palestinians don't have equal rights so I think I'm answering your question really clearly."