Threats for unspecified reasons given through this number.

Message from caller claiming to be from IRS criminal investigation.  Need to call ASAP.  Called number, and the voice message said to leave last 4 digits of SSN.  

An elderly gentleman called me at my government job, and told me the IRS had called him from this number and was going to send him to jail.  I came to this website and was able to assure the gentleman the call was a scam.  Believe me, this website does make a difference in people's life.

Threatened to have legal action taken against me by the IRS if I don't call back soon.  
How can they get away with these calls?

Most of these calls are from India and Pakistan.  

http://www.irs.gov/uac/Tax-Scams-Consumer-Alerts
http://800notes.com/forum/ta-8c2f64bf2b91fa5/irs-warns-of-telephone-scam

Report the Calls to the real IRS here:
•report the incident to the Treasury Inspector General for Tax Administration at 800-366-4484.
•You can also file a complaint with the Federal Trade Commission at FTC.gov. Add "IRS Telephone Scam" to the comments in your complaint.

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Do consider getting a call blocking device or phone.. You can google them and many are around $50.00 or so.If its a cell phone, some already have call blocking, if not, there are free apps on the web that will work for some. You can google this. If you have a smart phone, there is a free app called call control. Iphones appear to have apps also. Another one is called Mr. Number.