Would it not be illegal at literally any point? If you make one dollar or a thousand, the IRS wants to know. Maybe you meant at what point they would investigat

Would it not be illegal at literally any point? If you make one dollar or a thousand, the IRS wants to know. Maybe you meant at what point they would investigate, but that's dependent on too many factors for me (not an American) for me to even guess at. Perhaps the easiest way to gauge it is "If I earned this much in tips as a server, would I likely report it?"