From an audit report by Social Security's Office of Inspector General (OIG) (footnotes omitted, emphasis added):
Because the Social Security Administration (SSA) calculates future benefit payments based on the earnings an individual has accumulated over his/her lifetime, it is critical that the Agency accurately record those earnings. SSA’s ability to do so, however, depends, in part, on employers and employees correctly reporting names and Social Security numbers (SSN) on Forms W-2, Wage and Tax Statement. SSA uses automated edits to match employees’ names and SSNs with Agency records to ensure it properly credits earnings to the Master Earnings File. SSA places wage items that fail to match name and SSN records in its Earnings Suspense File (ESF). ...
[W]e obtained ESF data for TYs [Tax Years] 2007 through 2009. These data represented the most complete tax data available at the start of our audit, given the inherent lag in posting annual wage information. We then identified the 100 employers who contributed the most wage items to the ESF for the 3-year period. We also identified the 100 employers (with a minimum of 100 employees)who had the highest percentage of suspended wage items for TYs 2007 through 2009. For the 200 employers selected, we analyzed ESF data to identify reporting irregularities, such as SSNs that SSA either had never issued or assigned to another individual. We also contacted Employer Service Liaison Officers (ESLO) to obtain information on their experiences with employers who provided names and/or SSNs that did not match SSA’s records. ...
For TYs 2007 through 2009, the 100 employers who had the most suspended wage items had submitted over 2.3 million wage items for which the employees’ names and/or SSNs did not match SSA’s records. These wage items represented $15.7 billion in suspended earnings over the 3-year period. In total, 18 percent of the wage items these employers submitted did not match names/SSNs in SSA’s files. ...
In previous reports, SSA acknowledged unauthorized noncitizens’ intentional misuse of SSNs has been a major contributor to the ESF’s growth. SSA staff told us employers hired unauthorized workers because nothing prevented them from doing so. That is, employers know SSA had no legal authority to levy fines and penalties, and they were not concerned about potential IRS sanctions. Several of the employers and industry associations we contacted acknowledged that unauthorized noncitizens contributed to SSN misuse. For example, one employer told us his and many restaurants would close if they did not hire unauthorized noncitizens. A temporary labor service employer acknowledged that some of his former employees were unauthorized noncitizens who used invalid, unassigned, and deceased individuals’ SSNs. Furthermore, the president of a large growers’ association stated that farm labor contractors employed a large number of unauthorized noncitizens.The offending employers are not named in the audit report.