These calls are not coming from the IRS or anywhere else in the US government.
Here is a story from FOX 13, Tampa Bay, Florida about these calls. It's the best explanation I've found so far of these calls as well as what to do when you receive one and to whom to report the call and how:
202-241-4319 - They are very careful to NOT say they are with the IRS or the federal government.. They say "client investigation division" but division of what? He's " Agent Jim Arthur" but he doesn't say of what. He says he's investigating fraud & misconduct. I suspect our next call will threaten to arrest us, lol. Thank goodness for this board. I just worry about the naive people falling for this.
Got a call this a.m. from a man purporting to be from the Treasury Dept. & giving me the arrest warrant # for my tax fraud. Called himself Kevin Marsh, an unlikely name for someone who sounds as though he's from India. His # is 202-241-4319.