After a few Google searches, I verified that the return address does belong to the Social Security agency. So this letter is legit, but you need to make sure if you receive something similar to this letter, to always verify.
This particular form is apparently attempting to correct discrepancies. Your employer may have submitted the incorrect name for your social security credits. If it's not corrected, you would not receive the proper amount in your SSN account.
Here's the official description from FedForms.gov:
Request for Self-Employment - SSA needs the information collected on Forms SSA-L2765, SSA-L3365, and SSA-L4002 in order to credit the reported earnings to the proper earnings record. When W-2 wage data for an individual cannot be identified, the data are placed in the earnings suspense file, and SSA sends decentralized correspondence (D?COR) to the employee (and in certain instances to the employer) in an attempt to obtain his/her correct name and SSN. If the respondent furnishes the name and SSN information which agrees with SSA's records, or provides information which resolves the discrepancy, the reported earnings are added to his or her Social Security record.
While this particular inquiry letter proved to be real for me, that may not be the case for you. Always, always, always, verify if it is a scam. People are always attempting to get your identity in one way, shape or form.