The 2015 enactment of the Fixing America’s Surface Transportation (FAST) Act gave the Internal Revenue Service the authority to start revoking or denying passport applications of taxpayers with ‘seriously delinquent tax debts’.
‘Seriously delinquent tax debt’ involves tax debt of more than US $50,000, for which a Notice of Federal Tax Lien, or a Levy has been issued. In addition, it involves debt on which the time frame for the taxpayer to challenge the lien or levy by the taxpayer has expired.
From January 2018 the Internal Revenue Service will enforce the rule via the Department of State.
 Applies to taxes under Title 26 of the United States Code and includes interest and penalties but not FBAR penalties. The amount of $50,000 is indexed yearly for inflation.