An excellent study released by the Migration Information Source this month discusses how Italian Prime Minister Silvio Berlusconi addressed this disagreement: by issuing residence permits to 22,000 Tunisians, thus permitting them to move freely throughout the EU. France, home to many Tunisian migrants and citizens of Tunisian origin, responded by closing its borders with Italy and checking travel documents on trains coming from Italy. Though the French and Italian heads of state subsequently met and reconciled, and EU states have since unanimously expressed their support for Schengen, there is increasing political pressure to create a mechanism to respond to similarly "exceptional circumstances" -- a mechanism that would include the reestablishment of internal border controls.
As with the troubles with the Euro zone, Greece is viewed as a major source of Schengen tension. Lacking sufficient infrastructure to manage its rather extensive external borders, Greece has allowed large numbers of unauthorized migrants to enter Europe. Its current economic situation can only decrease Greece's ability to monitor its borders and increase the impetus for migrants arriving in Greece to travel elsewhere in Europe. Given the economic woes currently faced by the rest of Europe, this lax enforcement is not likely to be welcomed. Will Greece be the first country to be expelled from the Schengen zone? That remains to be seen, but the tensions between northern and southern members of the Schengen agreement are far from resolution, and may be exacerbated if bailouts become a southern European trend.