The big macro can cause big moves in the market. What does today's headline macro news mean for your portfolio?

What's happening: It's no longer Halloween, but markets around the world have gotten quite a fright from Greece as Prime Minister George Papandreou called a referendum vote on the brand-new bailout for the country.

In plain English, please: The move is largely seen as a political gambit, as Papandreou seeks to win back some support while his government struggles against populist anger over austerity measures. The hope is that the government can frame the question so that voters recognize that accepting the bailout and continuing with austerity is the only path to staying in the eurozone, which is something that most Greeks support.

The markets, however, are concerned that the referendum could lead to a rejection of the bailout or a call for new elections. That could lead to a disorderly default by Greece on its debt and the country's exit from the euro -- a scenario that could cause significant market dislocations and encourage bets against other struggling eurozone countries like Italy and Spain.

Stocks to watch: Direct exposure to Greece is obviously an issue in light of this, and U.S. investors should be chiefly concerned with National Bank of Greece (NYSE: NBG). However, as the scope of concern broadens out to the rest of the eurozone, investors may increase bets against companies like Banco Santander (NYSE: STD), Telecom Italia (NYSE: TI), Ryanair (Nasdaq: RYAAY), and Portugal Telecom (NYSE: PT).

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