Yeah, just received a call with the same message. To call them back at 310-929-8451.
Rest assured that IRS will never call you, period, let alone with a threatening message for you to call them back. I think a lot of these outfits are operated from outside of USA (thus the accent). Even if someone traced down to where they are, they can't be touched (or the cost of pursuing them is prohibitively high).
I received a couple of calls from this number (3109298451) saying the IRS has filed a claim against me. The voice was very mechanical. I have ignored it.
message says "This is the reason of the call is to inform you that we have filed a lawsuit against you for more information. Call immediately our department number 310 920 9 800 450 one I repeat 3998451."