As a non-profit organization based outside the US, what documentation is required to obtain a fee waiver?

For most non-profit organizations, we generally require a letter or other documentation from the local taxing authority to validate non-profit status.  However, in some rare cases, this may not be available in the Partner's local jurisdiction.  In such a case, we would require a document on official company letterhead (of the Partner) signed by the CEO or other head functionary indicating that they operate as a non-profit organization and have done so for XX years and are recognized by the local authority of competent jurisdiction to be such.