>SSNs are not universal, either. There are some unions and religious groups that have legal exemptions. Exempt from participating in social security (the progr

>SSNs are not universal, either. There are some unions and religious groups that have legal exemptions. Exempt from participating in social security (the program), not exempt from having a social security number. In fact, getting a social security number is the first step in applying for an exception from social security. Basically, SSA needs to track you as being exempt from social security, which requires a unique identifier.