Well, they are located in India and Pakistan and as such beyond the reach of US law.  Invest in a call blocker.

I got at least 3 calls from these people.  They left messages about being sued by the IRS.  I finally called them.  Yes, I am being sued by the IRS.  Yes, I have not responded to multiple mailings they have sent out.  I told the guy to send me another mailing and this time I will respond.  Then he hung up.  This is the worst scam I've seen yet.  I can't believe that anyone could fall for this, but I guess some people do.

Terrible to receive this on a recorded call.   I was then aware that there would be proper notification if this were a legitimate call.   People who do this activity need to realize the horrible impact that this has on others...and action taken on them for imposed stress they are causing.

I also received this Automated system saying they are the IRS and I'm being sued.
I've dealt with the IRS in the past. They do not phone you. They contact you through mailings.

Got the call today!! How stupid do theythink we are. Shows you how stupid they are!!!!!