The Blood Transfusion Service has apologised after 120 members of the Indian community were turned away from giving blood.
The blood drive was organised specifically for the Indian community last year, but confusion over criteria meant many were unable to donate.
Community leaders said they were left feeling “hugely embarrassed”.
The Northern Ireland Blood transfusion Service (NIBTS) said there had been a “breakdown in communications”.
“NIBTS fully accepts and apologises for the upset and inconvenience caused to those who attended the session and were unable to donate,” it said.
It said the error was caused by confusion regarding “travel criteria for donors” , and said “lessons learnt have been disseminated across the organisation to the relevant staff”.
The BBC has obtained a copy of an internal report and staff e-mails from the NIBTS, through a freedom of information request.ne
Umesh Vijayam helped to organise the event, which took place last year, and said people had travelled from as far away as Londonderry, Bangor and Newry to take part.
“Around 30 people had already arrived, with many more on their way,” he said.
“One of my friends went in to donate blood, he was very enthusiastic, he was first.
“They asked had he taken a malaria test since he was from India, a malaria-risk country.”
Dr Vijayam said it was then that they realised that there was a problem.
Surendran Varma was also one of the group that organised the event and said that the community “wanted to do something unique”.
Mr Varma said they had been campaigning for almost 10 months to recruit Indian donors by handling out pamphlets at three or four big Indian community events.
“It was the first blood drive for the Indian community and many people were excited,” he said.
He said that many people had taken a half day off work to donate blood and they planned to have a celebration meal afterwards.
Varma said it was “really shocking and embarrassing” when they were told they could not donate.
“Initially it was annoying, why did they not communicate with us what was needed?” he said.
“I had to call all my friends that hadn’t arrived and tell them not to come.
“They didn’t check our passport to see if we were an Indian citizen or a British citizen. They just looked at our face.
“They never checked if you had travelled to India, it was just a blanket ‘no’.”
The emails between the former donor services manager, Charles Kinney, and the organisations medical director, Kathryn Maguire, point out that the organisation should have anticipated the problems in advance.
A NIBTS spokesperson told the BBC all donors were assessed individually and some Malarial Antibody Tests (MAT) were taken.
They have also clarified some of the criteria for Indian people to donate blood:
NIBTS said that for all other donors, if it had been between four and 12 months since their return from a malaria-endemic area, a validated test for malarial antibody must be performed.