They are stating they are the IRS and this is your last warning because a lawsuit is being filed against you.   It is a very robotic female voice.  It is a new scam.  I looked it up on a government webpage.  Don't believe it.  They are from Florida.

Someone called claiming to be a  IRS agent. And if money owned to them is not paid over the phone a warrant for arrest will be issued. I knew it was a scam when they told me to resolve this case I would have to fly to Washington D.C. with a criminal lawyer.