This is a legit IRS outgoing number. I am a revenue agent. The number may be spoofed. Only until very recently did the IRM (internal revenue manual) change to not allow cold calls for initial contact. Up until late last year we were to call and follow up with a letter. Now we send a letter first.
Use common sense, it may be legitimate. We never ask for payment over the phone or threaten arrest.
This scam is pretty serious, and I think it's a domestic scam. No idea whose behind it. But they are pretty brass. IRS has got to shut these people down.