Many people have been scammed by criminals calling them on the phone purporting to be from the IRS making various threats unless the targeted victim immediately pays alleged overdue taxes.  For years, I have been telling people that the simplest way to know that the person calling you is not from the IRS is to remember that the IRS will never initiate contact with a taxpayer about overdue taxes through a phone call.  But that has changed.  In 2016 I told you about a new law Congress passed requiring the IRS to use the services of private collection agencies to collect some outstanding taxes.  This law is flawed on many levels including, as was pointed out by the IRS Taxpayer Advocate Service, the fact that this program not only had been tried unsuccessfully twice previously, but also is not cost effective.  But from my perspective, perhaps the greatest problem with this new law is that it increases the likelihood of scammers being able to pose as tax collectors and lure unsuspecting victims into paying these scammers money.
The law has now gone into effect and the IRS is sending letters by regular mail to people whose overdue tax accounts have been turned over to one of the four private collection agencies authorized by Congress to collect overdue taxes for the IRS.  The IRS is also at this time warning people to be wary of people claiming to be working for one of these companies who are, in truth, just scammers.  Of course, the IRS did not give any concrete advice as to how to know if the caller is legitimate or not.
As I have often said, whenever you get a phone call, you can never be sure who is really on the other end of the line.  Even your Caller ID can be fooled by a technique called Spoofing by which it can be made to appear that your call is coming from someone other than the real caller.  It is for this reason that I advise you never to give out personal information such as your Social Security number or credit card information to anyone who calls you on the phone unless you have absolutely confirmed that they are legitimate.  In the case of a call from someone purporting to be collecting a debt on behalf of the IRS, you should not give them any information or agree to do anything on the phone.  Ask them to send you written information about the alleged debt and then call the IRS to find out if the debt is legitimate or not.
In addition, the debts assigned to the private collection agencies are tax debts that are many years old and about which the taxpayer would have been contacted by mail previously by the IRS.  Also, be aware that none of the Congress authorized collectors will ask you to make a payment by credit card over the phone and certainly not ask you to wire money or pay by an iTunes card or gift card as some tax scammers have done.