Anytime you and the government disagree on issues
concerning your taxes, you have a tax controversy.

This may involve a disagreement about how a transaction was treated
or whether or not it should have been reported on your tax return. Your
tax return may be selected for an audit, or after an audit has been conducted,
you may be dissatisfied with the results and wish  to appeal.

Maybe your tax return was filed late or not at all. You may even agree
that money is owed, but disagree as to how much is owed and how it is to be paid.