Same as other's, it's a scam. OH NO! A Lawsuit?? Panic! This is what they are trying to get you to do and react and call back, don't do it, report it on the sites listed in other posts, if enough people do that there's a chance they get shut down.
I've just got a call from the same number. A recorded message said that IRS was trying to reach me and that I must call them back immediately to avoid serious consequences. I don't recall the exact wording. I didn't call back. It's a scam all right.
Received a message stating they were from the IRS, tried to reach me several times and it would be the last time before a lawsuit would be filed. The IRS would not leave a message like this, it's a hoax, don't believe it or call them. If your unsure call the IRS directly.