Former Labour leader Jeremy Corbyn is due to appear in conversation with an actor who joked about Jewish toddlers having their “cute little horns filed off”.
The event is set to be held next month to protest against this year’s Conservative party conference.
Catastrophe actor Rob Delaney, 44, wrote in 2009, “When I think of adorable Jewish baby boys getting circumcised AND having their cute little horns filed off, I get so sad!”
The tweet from 12 years ago resurfaced on social media ahead of the October 4 event organised by the People’s Assembly.
Online users were quick to highlight other potentially inflammatory tweets by Mr Delaney, including one from 2011 that read: “Somebody probably has the phone number 1-800-JEW-FART.”
In another tweet from 2012, he also quipped about wishing to atone on Yom Kippur “for the weeks I’ve wasted on chubby naked Jewish girls on bikes dot com” and in 2012 described a single by rock band Van Halen as being “worse than 3 Holocausts.”
The tweets sparked an outpouring of criticism, with the Jewish Labour Movement’s national secretary, Adam Langleben, describing the posts as containing “crap and crude jokes about Jews”.
Mr Langleben also expressed concern about Mr Corbyn's participation in an event featuring Mr Delaney.
"What's funny is that Jeremy despite years of denials and problems still manages to share platforms with people who have said ridiculous and arguably racist things about Jews. Still. After all this. After everything," he wrote.
Some, however, came to Mr Delaney’s defence, suggesting the tweets were satirical, with one online user writing that the comedian “may be a Judeophile, rather than an antisemite”.
Mr Corbyn, who stepped down as leader in 2020, is currently not sitting as a Labour MP following his suspension last year over his reaction to a report into antisemitism in the party.
His tenure as leader was overshadowed by criticism of Labour’s handling of antisemitism allegations.
His successor Keir Starmer has vowed to root out antisemitism from the party and sought to mend ties with Jewish groups.
Mr Delaney has previously written about his relationship to the community, revealing in 2011 that he was Catholic but attended nursery school at a Jewish community centre as a child.
The comedian, who at the time was living in Los Angeles, said the Californian city had “even more Jewish people than Marblehead”, his hometown in Massachusetts.
“In fact, I wouldn’t even think of living somewhere that wasn’t swarming with Jews,” he wrote in the first-person piece published by Vice.
Mr Delaney’s management and the People's Assembly were approached for comment.