The IRS will send you a letter first.
They will not email you.
They will not text you.
They will not message you over social media.
In rare instances, they may call. But only after they send a letter.
The scumbags (the scammers, not the IRS) call and demand immediate payment for back taxes and threaten to get law enforcement involved if you don't comply.
Speaking from experience, it's a little rattling until you come to your senses.
And naturally, they target people around tax season.
So be careful out there.
And if you're looking for a laugh, have a little fun with them like this guy did.