From the Fiscal Times:
A new report by the Treasury Inspector General for Tax Administration released this week highlights the problem and suggests that the IRS may still be doing too little to go after employers suspected of hiding wages and failing to report billions of dollars in federal payroll taxes, including for Social Security and Medicare.
The inspector general analyzed 137,272 cases from tax year 2013 in which there was a glaring discrepancy between employee wage and withholding information reported to both the IRS and the Social Security Administration and found that the IRS declined to investigate most of the possible fraud. According to the inspector general, the IRS intervened in only 23,184 of those cases, or just 17 percent of the total. ...
And it's going to get worse since the IRS budget keeps getting cut, allowing abusive schemes to flourish.