Catalonia in northeast Spain will issue a challenge to the EU as regional leader Artur Mas prepares to ask voters to declare whether they want an independent state within the EU.
A Yes vote in the referendum would not just create a constitutional crisis for Spain, which has no mechanism for allowing the independence of one of its regions, but would also issue a clear challenge to the EU. The EU has no system for the break-up of a member state, and a new entity could have future membership blocked by just one member country.
Mr Mas said he planned to ask the question, including the reference to the EU, during a four-year term that starts after regional elections on November 25th.