European officials voiced concern on Thursday over Denmark’s plan to reintroduce customs controls on its borders, abolished under the Schengen Agreement. France and Italy have bickered over the entry of several tens of thousands of North African refugees while Greece is struggling to prevent illegal aliens from entering Europe from Turkey. The free flow of goods, people and services, heralded as one of the great achievements of European union, is in jeopardy.

Denmark reinstated customs patrols and introduced video surveillance on its internal borders with Germany and Sweden, supposedly to fight drug trafficking and transnational crime. While such measures are allowed temporarily under the Schengen Agreement, European Commission President José Manuel Barroso questioned the legitimacy of “intensive and permanent” border checks in a letter to the Danish prime minister.

A council of European interior and immigration ministers on Thursday suggested that the Schengen rules had to be clarified to prevent member states from unilaterally closing their borders.

All countries that belong to the European Union are required to implement the Schengen Agreement which eliminated border patrols and customs checks between member states in 1999. Ireland and the United Kingdom are exempt as are the overseas territories of Denmark, France and the Netherlands. Iceland, Norway and Switzerland, although not part of the EU, do belong to the Schengen Area.

Bulgaria and Romania, which were among the most recent of Eastern European nations joining the EU, won’t become full members of the Schengen Area until 2014 when all member states have to allow their citizens to work in whatever European country they want. Until then, Bulgarian and Romanian laborers are not welcome in ten Western European countries.

The recent influx of mostly Tunisian refugees from across the Mediterranean compelled Italy last month to issue special travel visa to an estimated 25,000 immigrants, dispersing them across the European Union. France responded by shutting its border with Italy, claiming that the migrant surge posed a threat to public order. Many Tunisians speak French and have relatives who live in the country.

Although Italy on average receives far less immigrants than the more prosperous Northwestern European member states do every year, the unrest in North Africa and subsequent refugee flow demonstrated the difficulty of securing Europe’s outer borders despite the Italian coast guard’s efforts to turn boats carrying refugees around. Frontex, the European border patrol agency, is also deployed in the Mediterranean and along the Greek border with Turkey where hundreds of illegal aliens attempt to cross into Europe every day.

Nations on the fringe of Europe complain that they are bearing the brunt of frontier security and want help from their fellow EU member states in securing the outer border. Others insist on maintaining existing treaty which prescribes that immigrants are the responsibility of whichever country they enter first.