You need the employment authorization as well as the social security card. Look at the i-9 form on USCIS to see which documents you can use. There's a column bank of documents you need to provide.
__________________
Renewal Delivered
06/17/2014
797c-----------------
06/23/2014
Biometrics letter --
06/30/2014 Done
06/30/2014
Expiration Date ---
09/11/2014
Approval Date ---
09/02/2014