A computer error has left about 10,000 UK supporters of Greenpeace out of pocket by hundreds of pounds.
Greenpeace has taken action to reimburse those affected
Some members who make regular direct debit donations, ranging typically from £2 to £10 a month, have been charged a hundred times their usual amount.
Greenpeace said those affected would be reimbursed by 3 January, and that any resulting bank charges would be paid.
The environmental charity said it seemed the glitch had led to two noughts being added to donations.
John Sauven, a Greenpeace director, said it had taken immediate action once the software error had been spotted.
"We are still trying to find out how this glitch happened but for some reason two noughts seem to have been added, or the computer has converted pence into pounds," he said.
"Our IT specialists are trying to work it out and rectify it to make sure it doesn't happen again.
"The only people who will be out of pocket are us."
According to Greenpeace's website, it receives donations from 221,000 supporters in the UK.