Since 1990, GAO has periodically reported on high-risk federal programs that are vulnerable to fraud, waste, and abuse. Two such high-risk areas are managing federal contracts more effectively and assessing the efficiency and effectiveness of federal tax administration. Weaknesses in the tax area continue to expose the federal government to significant losses of tax revenue and increase the burden on compliant taxpayers to fund government activities. Over the last several years, the Senate Permanent Subcommittee on Investigations requested GAO to investigate Department of Defense (DOD), civilian agency, and General Services Administration (GSA) contractors that abused the federal tax system. Based on that work GAO made recommendations to executive agencies including to improve the controls over levying payments to contractors with tax debt--many of which have been implemented--and referred 122 contractors to IRS for further investigation and prosecution. As requested, this testimony will highlight the key findings from prior testimonies and related reports. This testimony will (1) describe the magnitude of tax debt owed by federal contractors, (2) provide examples of federal contractors involved in abusive and potentially criminal activity related to the federal tax system, and (3) describe current law and proposed federal regulations for screening contractors with tax debts prior to the award of a contract.