I received a voicemail twice from this phone number with this same threat information. I'm glad to hear that this is just a scam and I'm glad that I did not call them back. Thanks for the heads up.
Received voicemail from unidentified accented person from this California number (i think landline) with no name and no organization saying call back that there is an IRS problem. I did not!
Caller ID said "IRS", caller claimed I owed back taxes from years ago and needed to make an immediate payment. They asked for a credit card to make payment, then hung up when I went to verify their number on Google.