It was billed as the ultimate London Purim party for young professionals, with tickets sold out and 1,000 people attending.
But guests at the Young UJIA event have complained of having to wait for over an hour-and-a-half for admittance to the venue, the Revolution Leadenhall club.
Having paid up to £30 a ticket, angry patrons accused the organising committee of partying inside the club rather than interceding with "aggressive" bouncers to speed up admissions.
UJIA claimed that "staff members were prevented from assisting with the queue by the security staff," an allegation denied by the club's general manager, Stewart Fairbrass, who said the 10 bouncers had faced a difficult situation. Despite a "happy hour" starting at 9pm, "80 per cent of people came after 11pm. It's a huge number of people at one time."
Mr Fairbrass added that a fast-track line had been abandoned because committee members did not have an accurate list of those who were eligible. "Ninety per cent of people who tried to queue jump were not on the list. That also slowed down the process."
The UJIA committee had been made aware that the terms of the club's licence required that "we have to have a scanning machine and ID everyone on the night". Anyone "too intoxicated" was denied admittance. "The street was littered with empty bottles. We spent over an hour clearing up afterwards," Mr Fairbrass said.
Among complaints posted on the event's Facebook page, Aryeh Citron wrote: "It was UJIA's fault. It was a UJIA event. They were responsible for instructing the club with guidelines for the bouncers and also should have had UJIA staff on the door to monitor what was going on." Adam Scott Murad said: "Fun event but the queue and security checks were a joke". Some more critical comments were deleted.
A UJIA spokeswoman reported that 20 complaints had been received, adding: "We want to reassure all those who attended that we are investigating these incidents as a matter of urgency. We completely understand that those affected will be feeling upset.
"The very small number of people who have requested refunds have been provided with them." The party raised £22,000 for the charity.