In the U.S. a Social Security Number is issued to track earnings over a worker’s lifetime. Scholars who are employed in the U.S. must apply for an SSN. International scholars who are unemployed are ineligible for an SSN.
If you have been previously issued an SSN from a previous time in the U.S., your SSN belongs to you and you do not need to request a new number.
An SSN is not an off-campus employment authorization and an SSN is not required to open a bank account, rent an apartment, start a mobile phone contract or get a credit card.