Labour leader Jeremy Corbyn has been criticised for attending an event organised by a left-wing group critical of mainstream Jewish organisations.
It comes hours after Mr Corbyn promised "watertight" investigations into claims of anti-Semitism within his party.
One Labour MP called his actions "irresponsible and dangerous".
On Monday, Momentum, the Labour movement backing Mr Corbyn, released a statement saying the party had "failed" on anti-Semitism,
Jewdas has accused the Jewish Board of Deputies, Jewish Leadership Council and Jewish Labour Movement of "playing a dangerous game" and previously dismissed anti-Semitism allegations as right-wing smears.
A spokesman for the Labour leader confirmed Mr Corbyn had attended the event, marking the Jewish festival of Seder, in a personal capacity and not on behalf of the party.
In a tweet, Labour MP John Woodcock said meeting the group gave the message that "extreme views are OK".
Skip Twitter post by @JWoodcockMP
This is deliberately baiting the mainstream Jewish community days after they pleaded with him to tackle antisemitism. And he must know that meeting them now will give his members the message that the group’s extreme views are ok. Irresponsible and dangerous https://t.co/NORQQiFq8J
— John Woodcock (@JWoodcockMP) April 2, 2018
End of Twitter post by @JWoodcockMP
Labour's Angela Smith said Mr Corbyn's attendance was a "blatant dismissal" of the case to tackle anti-Semitism in the party.
Meanwhile, the chairman of the Campaign Against Anti-Semitism, Gideon Falter, said Mr Corbyn's claims to remedy anti-Semitism within the party and his appearance at this meeting made him a "duplicitous" man.
The chief executive of the Holocaust Educational Trust, Karen Pollock, said on Twitter it was "mocking and disrespectful".
Skip Twitter post by @antisemitism
.@Gideon Falter, Chairman of CAA, said: “…It’s hard to imagine how this duplicitous man can claim to be remedying antisemitism within the @UKLabour Party. The Party must consider the message that is sent to British Jews and other minorities by @JeremyCorbyn remaining as Leader.”
— Campaign Against Antisemitism (@antisemitism) April 2, 2018
End of Twitter post by @antisemitism
The party has been engulfed in a row about attitudes towards the Jewish community after it emerged there was a backlog of some 70 incidences of anti-Semitism within the party that had not been dealt with.
Mr Corbyn has previously apologised for the "hurt" in the failures to address complaints and insisted the party does not tolerate anti-Semitism in any form.
Labour has dropped one council candidate over allegedly sharing posts on social media urging followers to "question the Holocaust".
Momentum's national co-ordinating group acknowledged the failure to deal with cases in a "sufficiently decisive, swift and transparent manner".
While it suggested that Jeremy Corbyn's opponents may be "opportunistically using this issue as a way to undermine his leadership", that did not diminish "our responsibility to challenge anti-Semitism whenever and wherever it occurs".
Later, the party's new general secretary will start her role to ensure allegations of anti-Semitism are dealt with effectively.
In an interview with Channel 4 News, Mr Corbyn said the issue would be a top priority for Jennie Formby and insisted "absolutely strong and watertight" investigations would take place.