As Europe scrambles to contain the financial crisis in the eurozone, another effort to deepen European unity is also being challenged, the Schengen passport-free travel zone.
Immigration, lax controls, corruption and sovereignty worries are undermining dreams of border-free travel.
Europeans now take for granted using the euro across the 17 countries sharing the currency. They also rarely think twice about crossing the borders of more than two dozen European nations without showing their passport. Launched more than a decade ago, the so-called "passport-free travel" Schengen zone now includes 25 nations, including some, like Switzerland and Norway, which are not part of the European Union.
European Home Affairs Commissioner Cecilia Malmstrom, who wants to set new rules for Schengen, argues its benefits are enormous.
"I think there is a general agreement about the importance of Schengen and the possibilities it gives for the citizens of the European Union and the Schengen member countries to travel freely, and we must really safeguard this fantastic achievement," said Malmstrom. "It is also something really important for business, and it has facilitated life, and it has brought us huge benefits."
But today, Schengen's viability is being questioned. Last week, its members blocked Romania and Bulgaria from joining because of concerns they were not doing enough to fight corruption, crime and illegal immigration. Immigration fears are also eroding support for Schengen in countries that already belong like Spain, Germany, Denmark and France.
France, for example, reinforced controls on its border with Italy earlier this year to staunch a wave of illegal immigrants from North Africa. It joined Spain and Germany in expressing concerns about handing the European Union more say over Schengen.
The bottom line, says Brussels-based immigration expert Hugo Brady of the Center for European Reform, is a lack of trust.
"The politics of the Schengen area is that everyone wants more control over other people's borders while maintaining the same amount of control over their own... and that's the paradox of the matter," said Brady.
Today, anti-immigration politicians like European deputy Bruno Gollnisch of France's far-right National Front Party, are gaining public support with arguments that Schengen must either be tougher, or scrapped altogether.
"In France, we already have millions of immigrants and many social problems, and I think the country is absolutely crowded now… [in] the suburbs and big cities and we should have a different policy. Not only about people who come, but to try to - by cooperating with the original country - to have some of them at least going back home," said Gollnisch.
Greece, which is at the heart of the European debt crisis, also has Schengen's most porous borders. Experts say the vast majority of illegal immigrants cross its border with Turkey. For the moment, the European Union's Frontex border control agency has been shoring up the Greek border. Athens shares no land border with other Schengen countries, hampering immigrants' efforts to move on.
Even as Greece's debt crisis has shaken European confidence, Brady says, so has its immigration problem.
"If the eurozone breaks up - which is now looking like a possibility - the resulting political and economic calamity would also spread to other major projects like Schengen," noted Brady. "They would say, 'basically these people (the Greeks) have destroyed the next 10 years, how the hell would we trust them with something so sensitive as borders and immigration policy?'"
Brady believes European nations need to revamp Schengen and establish a better border monitoring system. While the prospects appear unlikely of dismantling the passport-free zone anytime soon, he says doing so would have a devastating impact on Europe's tourism and economy, just as the region is trying shake off the financial crisis.