This is a SCAM!!! The recording of a computer voice leaves a message, stating that the I.R.S. has filed a lawsuit against you. Don't fall for this! The real I.R.S. will NEVER contact you this way! If there were a real lawsuit against you, they must notify you by mail at least twice. Also, a subpoena to appear in court must, by law, be delivered to you in person.
If you have any doubts, call your local I.R.S. office yourself and inform them of the phone call you received. I am positive, they will tell you that it is a scam.