The Northern Ireland Council for Voluntary Action has said it opposes the unofficial charities' register launched in February.
The 'register of approved charities' has been set up by the company Social Investment Exchange to help Northern Ireland's non-profit organisations get more business funding.
To join the register, charities must pay £200 a year and demonstrate they are legal, accountable and transparent.
But Nicva has distanced itself from the venture after getting several queries from members asking if they should join.
Its chief executive, Seamus McAleavey, said: "This is a private sector initiative which Nicva does not support. It is not a Government or statutory initiative and, therefore, does not have any regulatory authority as its name would imply. We do not have registered charities in Northern Ireland but rather we have organisations that are treated as charities for tax purposes."