Len McCluskey, the leader of the Unite union, has attended an event at the Labour Party conference hosted by an anti-Zionist group opposed to a rule change that will make antisemitism within the party a punishable offence.
Mr McCluskey made an appearance at the event hosted by the Jewish Voice for Labour group on Monday evening - even though his union is supposed to be backing a Jewish Labour Movement rule change motion on antisemitism in the party.
The union leader was seen at the back of the hall at the Mercure hotel in Brighton watching on as a series of speakers attacked Israel and claimed antisemitism was a smear tactic used by opponents of Jeremy Corbyn.
Also present at the inaugural meeting of the group were Jackie Walker and Tony Greenstein - both currently suspended from Labour over antisemitism allegations.
One source told the JC:"It was a real shock to see Len McCluskey at the JVL event.
"Make no mistake about it - this was a hardcore anti-Zionist event.
"Unite are one of the unions on the party's NEC who have given unanimous backing to the JLM rule change motion that is being debated on Tuesday morning.
"But Mr McCluskey seems to be sending out completely the opposite message."
Speakers at the meeting, which attracted around 250 people, included Naomi Wimborne-Idrissi, a veteran Jewish anti-Zionist campaigner, and Jewish Socialist Group member David Rosenberg addressed the crowd of around 250 people.
Sources told the JC that organisers of the JVL meeting attempted to shut down any filming or recording of the event.
The Jewish Voice For Labour group claim to offer "a space" for "progressive Labour Jews."
In a leaflet they state: "We uphold the right of supporters of the justice for Palestinians to engage in solidarity activities, such as BDS.
"We oppose attempts to widen the definition of antisemitism beyond its meaning of hostility towards or discrimination against Jews as Jews."