Charities are not subject to the federal "Do Not Call" registry. However, paid solicitors are subject to the Federal Telemarketing Sales Rule, which provides that the paid solicitor must maintain a charity specific "do not call list".
The caller can simply say, "thank you for calling, but please add my name to your do not call list". This applies only to the particular charity that the paid solicitor was calling about. You may get calls from the same paid solicitor on behalf of other charities. If they continue to call after an appropriate waiting period, they are in violation of the federal law.