Liberal Democrat president Simon Hughes has been strongly criticised by the party's Friends of Israel group for signing a virulently anti-Israeli early day motion.
LDFI secretary Matthew Harris also castigated the anti-Zionist group that the EDM welcomed.
The motion from Hayes and Harlington Labour MP John McDonnell praised the new International Jewish Anti-Zionist Network, saying that it "gives voice to the great and growing number of Jewish people worldwide who refuse to allow the Israeli state to act in their name and who condemn Israel's ethnic cleansing of Palestinian people, including the murder of 64 children in 2008 alone, its apartheid laws, its expropriation of Palestinians' land and resources, its militarism and nuclear weapons, and its trade in arms (the fourth largest in the world); and notes that by speaking out IJAN discredits Israel's attempts to suppress criticism with false accusations of antisemitism".
Mr Harris said: "I deeply regret Mr Hughes's decision to sign this EDM which is out of step with LibDem policy and with the constructive approach that he took previously on this conflict. It is very disappointing because he has always been a well-balanced, critical friend of both Israel and the Palestinian people.
"We had drawn to his attention the appalling nature of IJAN and the disgusting things they say in their charter. One can only assume that Mr Hughes thought wrongly that IJAN was a group of constructive Jewish critics of Israel with something useful to add.
"There are small liberal Jewish organisations that raise issues and perhaps Mr Hughes thought it was one of those, but they are not."
Simon Hughes did not respond to requests to comment.
Board of Deputies' chief executive Jon Benjamin said: "This EDM contains a particularly nasty form of words and shows a complete disregard for balance, truth or the fact that many Israelis and Jews around the world work tirelessly for peace and understanding, without demonising one side to the conflict or the other.
"The signatories are making an unequivocal statement that Jews have no right of self-determination and that they [the signatories] have swallowed, hook, line and sinker, the most extreme calumnies of the anti-Zionist cause."
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