Total scam.  Originates in either India or Pakistan.  
See:  http://www.irs.gov/uac/Newsroom/IRS-Reiterate ... -Telephone-Scam

Report them:
http://www.treasury.gov/tigta/contact_report_scam_ok.shtml

IRS does not file lawsuits.  Tax disputes are civil matters.  90% of all IRS tax disputes are settled administratively.  IRS has absolutely no authority to call on local law enforcement for anything. Local law is never involved in IRS tax disputes.   If LE is necessary, US Marshals do the job.  IRS does not cold call anyone and ask for money.  All  contacts by the IRS are initiated by US mail.