20 CFR 404.1035
§404.1035 Work for a communist organization.
If you work as an employee of an organization which is registered, or which is required by a final order of the Subversive Activities Control Board to register under the Internal Security Act of 1950 as a communist action, communist-front, or communist-infiltrated organization, your work is excluded from employment. The exclusion is effective with the calendar year in which the organization is registered or the final order is in effect.
You probably have to pay income and SS taxes. But such work doesn't count towards your SS qualification.