The US federal government has mandated that all legal residents and citizens must have a valid social security card. The card, with a valid Social Security Number (SSN) is used by the Internal Revenue Service (IRS) to track of an individual's yearly wages and taxes owed and employers are required to note this number on the payroll system. A valid social security card may be required for other financial transactions including while opening bank accounts, applying for loans, getting phone/electrical service, a driver's license..the list goes on and on. Yes, you can live without it, but it's a huge pain in the ass.