EU: The Lisbon Treaty, Article 50; EU, EMU and Eurozone Membership; Greece Court Injunction and Legal Action?

From The EU Lisbon Treaty

Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.

EU Membership is one thing; membership of the EMU/Eurozone is quite another: see the treaty (pdf online), eg

TREATY ON STABILITY, COORDINATION AND GOVERNANCE IN THE ECONOMIC AND MONETARY UNION 

BEARING IN MIND that the need for governments to maintain sound and sustainable public finances and to prevent a general government deficit becoming excessive is of essential importance to safeguard the stability of the euro area as a whole, and accordingly, requires the introduction of specific rules, including a "balanced budget rule" and an automatic mechanism to take corrective action

RECALLING that the Contracting Parties, as Member States of the European Union, are to refrain from any measure which could jeopardise the attainment of the Union's objectives in the framework of the economic union, particularly the practice of accumulating debt outside the general government accounts...

NOTING that compliance with the Contracting Parties' obligation to transpose the "balanced budget rule" into their national legal systems, through binding, permanent and preferably constitutional provisions, should be subject to the jurisdiction of the Court of Justice of the European Union...

The Guardian, Greece and the Eurozone - Europe's big guns warn Greek voters that a no vote means euro exit - "Germany, France and Italy joined the European commission in insisting that Sunday’s poll is about continued eurozone membership"

Greece threatens European Court of Justice action re Grexit (The Telegraph) -

'Greece has threatened to seek a court injunction against the EU institutions, both to block the country's expulsion from the euro and to halt asphyxiation of the banking system. “The Greek government will make use of all our legal rights,” said the finance minister, Yanis Varoufakis.
“We are taking advice and will certainly consider an injunction at the European Court of Justice. The EU treaties make no provision for euro exit and we refuse to accept it. Our membership is not negotiable,“ he told the Telegraph.'

Kathimerini item - Βαρουφάκης: Προσφυγή στα Ευρωπαϊκά Δικαστήρια, αδιαπραγμάτευτη η θέση μας στην Ευρωζώνη

Financial Times - Eurozone leaders take co-ordinated gamble with response to Athens

New York Times - Can the United States Prevent a Grexit?

Business Insider/ Reuters: A return to the drachma? A Greek lawmaker reportedly has a team preparing the groundwork for a return to the drachma

Bloomberg - Greece Can Stay in Euro Even With ‘No’ Vote, Schaeuble Tells Lawmakers

On Eurozone issues

On EMU and the Euro (legal issues)

Legal and political texts, January 1999

ESM Treaty (European Stability Mechanism)