The European Commission has ordered Apple to pay 13 Billion Euros (~$16 Billion USD) in back taxes to Ireland as a result of a back tax judgement from August 2016. Apple stock fell 1.40% today and will likely fall further as the news spreads.
The above diagram shows how Apple avoided billions in taxes over the years by getting special treatment in Ireland.
"We now find ourselves in the unusual position of being ordered to retroactively pay additional taxes to a government that says we don't owe them any more than we've already paid,"
Apple CEO Tim Cook
Both Ireland and Apple are appealing the order and there is a good chance they will win and go back to not paying taxes while many of us pay as much as 45% taxes.