Concern Worldwide: Charity error affects 6,000 Northern Ireland donor accounts
Concern Worldwide has apologised for taking 100 times the normal donation amount from some of its supporters' bank accounts.
About 6,000 of the charity's donors in Northern Ireland were affected by the "administrative error".
Concern says it will pay back the money taken and any bank charges incurred.
A total of 24,700 people across the UK were affected. Supporters of the charity in the Republic of Ireland did not experience the error.
The charity's UK executive director, Rose Caldwell, said: "We apologise unreservedly for the error and any problems this may have caused".
"As soon as we became aware of the problem, we took immediate action to rectify it by contacting donors directly.
"We are conducting a rigorous investigation into how this error happened to ensure it will never happen again.
"Without the support of our donors, Concern would not be able to deliver its life-saving humanitarian work to vulnerable people worldwide."
The organisation is urging those affected to get in touch with their bank as soon as possible to process what is known as an indemnity claim - the fastest way to be refunded.
If for some reason people cannot file an indemnity claim, then Concern says it will process the refund.
However, that method will take longer.