iPhone with EU flag in the background.
The European Union has levied a fine against Apple; its stock declined.
  • Apple's stock fell Monday morning after EU regulators slapped the company with a $2 billion fine.
  • The fine is part of the EU's push to get Apple to open up its App Store.
  • Investors are trying to figure out how much opening the App Store may hurt the company long term.

European regulators have fined Apple $2 billion for violating antitrust rules.

But that's not the worst news Apple is dealing with Monday.