The IRS recently announced that it will begin contacting people regarding back taxes through private debt collection agencies. However, these private collection agencies will only be used for limited types of cases. However, with any entity that tells you it is working on behalf of the IRS, it is still wise to question the contact's validity—many people claim they are “working on behalf of the IRS” as part of an IRS scam.
Still, with this new change, there are ways to protect yourself if you are contacted by a legitimate private debt collector.
Details of the Initiative Using Private Debt Collectors
...