 The IRS collects a billion dollars in overdue tax revenue after launching a crackdown on millionaires not paying what they owe. The agency targeted 1,600 individuals last fall with more than a million dollars in annual income and more than $250,000 in tax debt. Audit rates for high-wealth individuals fell over the last decade and have been at historic lows. But IRS Commissioner Danny Werfel says the IRS is staffing up and using tools like artificial intelligence to beef up enforcement.