The European Commission is considering plans to re-introduce border controls that had been eliminated under the Schengen agreement in 1985.
The proposed new rules have been drawn up to address mounting concern in parts of Europe over illegal immigration, notably from North Africa.
Under Schengen, visitors with a visa for one participating country can travel freely throughout the zone which includes 22 of the 27 EU member states, as well as Switzerland, Norway and Iceland.
Ireland, the UK, Bulgaria, Romania and Cyprus are not part of the accord.
If implemented, border checks could be restored, if member states persistently fail to protect the EU's external frontier.
Critics point to Greece in particular, largely because of persistent surveillance problems on its border with Turkey.
France and Denmark sparked controversy this year by unilaterally re-introducing controls.
The Brussels plan proposes taking away decision-making from national governments and giving more say over travel curbs to the EU executive and EU states as a group.
France, Germany and Spain have already voiced opposition to the move.
Debates across Europe over immigration and border controls intensified this year when popular revolts in Tunisia and Egypt and a civil war in Libya raised concerns that hundreds of thousands of illegal workers could seek refuge and jobs in Europe.
Up to 30,000 people have ended up reaching European shores, mostly Italy's, but concerns that borderless travel facilitates illegal immigration remained.
