Three charities fear they have lost reserves totalling £25m in the wake of the banking collapse in Iceland.
Stephen Bubb, head of chief executives body Acevo, said three members had contacted the organisation with concerns that their reserves in Icelandic bank accounts could be lost.
The unnamed organisations held reserves of £11m, £10m and £4m respectively in Icelandic bank accounts.
"We have had reported to us today potentially lost deposits of £25m," said Bubb. "The position at the moment is that they have lost the money."
Bubb said he had asked Chancellor Alistair Darling to extend to charities the protection offered by the Government to individual savers. "The Government must act now to save charities and the people they support," he added.
The NCVO said it had also fielded calls from members concerned about the situation in Iceland.
The umbrella body said it would be seeking assurance from the Government that its members' money was protected. It has called for November an emergency meeting of leaders from across the sector to discuss the crisis.
Stuart Etherington, chief executive of the NCVO, said: "We need to come up with a robust plan about what is currently happening and, more importantly, how we go forward together in what look like difficult times ahead."