STREET ADDRESS (No PO Box, RD or RR). It is not illegal for an employer to ask you for your social security number (SSN).HOWEVER you are in no way obligated to provide your SSN. Not all forms are listed. We are writing to you because we believe you may have recent work activity and we need to know more about this work activity. Your Form I-766 to prove your immigration status and that you can work in the U.S.. •. Your birth certificate to prove your age. The Work History report asks that you write down all of the jobs you have had in the last 5 years. Legitimate employers will require you to provide both your SSN and a photo ID when they fill out the I9 form. At that time, you should simply complete a new Form I-9 with your updated SSN and original hire date.