It's a scam - leaves a partial message that you're the subject of an IRS lawsuit and to call them to get info on the case file. [***]. If the IRS wants to talk to you, they'll contact you personally by mail first. Don't bother with these clowns.
Have received multiple calls from different numbers, always leaving the same message: Received call, didn't answer, went to voicemail and message left that it was the IRS, my last warning they are after me, call back. I blocked the number. I've clearly received too many final warnings. (Sarcasm in last sentence...)