Congress passed a bill on on December 3, 2015 called the Fixing America's Surface Transportation (FAST) Act (H.R. 22). The bill contains two IRS provisions (that were kinda tacked on quietly) that allow the IRS to use private debt collectors, and would revoke passports for taxpayers with more than $50,000 in unpaid federal taxes.
The Taxpayer Advocate actually found that the IRS was better at collecting taxes than private debt collection agencies, and then there is the whole issue of taxpayer privacy. Collection agencies are notorious for disregarding privacy law, but that's not even the worst part of this news.
The worst part is that the LAST time Congress tried to outsource IRS collections, the collection agencies cost taxpayers more money than they collected, which means that private collection of IRS debt is a failed experiment that congress has decided, unfortunately, to repeat.