It’s all about Form 323, which adds a requirement of an FCC Registration Number (FRN), to obtain which requires individuals to provide their Social Security number.
Until the matter is sorted out, the Commission is offering a “Special Use” FRN, not based on a taxpayer ID or Social Security number, available only to a person who is “unable to obtain or does not have permission to use an SSN, after using diligent good-faith efforts.”