Pursuant to a congressional request, GAO reviewed whether the Internal Revenue Service (IRS): (1) accurately cross references the two identification numbers that self-employed individuals report on their tax returns; and (2) needs to take any actions to improve the accuracy of its cross-reference files.

GAO found that IRS: (1) uses information from different computer files to identify sole proprietors that may have tax compliance problems; (2) requires certain taxpayers to have a valid social security number (SSN) and employer identification number (EIN) so that it can cross-reference the taxpayers' accounts from one file to another; and (3) records a sole proprietor's identification numbers on three computer files and uses the SSN to establish an account on the Individual Master File. In addition, GAO found that: (1) the identification numbers that IRS records for cross-referencing purposes are not always reliable and cause IRS to generate false underreporter leads; (2) the IRS computerized screening process limits the number of false underreporter leads created by the Cross-Reference Entity File; and (3) if IRS and the Social Security Administration eliminate sole proprietors' EIN, they will have to modify their computer programs to accept SSN instead of EIN.

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