A new report is shining light on a problem at the IRS that could impact millions of those who enjoy gambling: a huge gap in tax collections and compliance when it comes to unreported winnings. The amount? $13.2 billion.

Sports betting and online gambling in the U.S. has increased in recent years. To address the revenue that might be left out due to underreporting, the Treasury Inspector General for Tax Administration (TIGTA) audited the IRS for signs of missed gambling winnings.