Adding border checks to Europe's passport-free area would cost 3 billion euros ($3.3 billion) a year in lost business, the bloc's chief executive said on Wednesday, seeking to reinforce a message that impulsive measures to curb migrant flows would hurt the economy.
With some 1.7 million workers crossing EU internal borders every day and with 57 million journeys made across those frontiers every year, European Commission President Jean-Claude Juncker said every hour of waiting time at borders had a cost.
"One after another, we close the borders and once they are all closed we will see that the economic cost is huge," Juncker told the European Parliament in Strasbourg.
"If we close the borders, if the internal market begins to suffer ... then one day we will be wondering whether or not we really need a common currency if there is no single market, no free movement of workers any more," he said, warning of the threat to the euro.
Juncker, whose EU executive is working on revising the bloc's asylum and migration policy, said he decided to stress the economic impact because of EU governments' "cavalier" attitude to the Schengen zone of passport-free travel.
Though 3 billion euros is a relatively modest amount in terms of annual trade in goods among the 28 EU member states that is worth some 2,800 billion euros, Juncker and German Chancellor Angela Merkel have both linked the future of EU's single currency to border closures in recent weeks.
In an apparent shock tactic to combat strong nationalistic reactions to migration, Juncker warned last week in his first news conference of 2016 that citizens would find it harder to find jobs and said that the euro "made no sense" in a Europe where people could no longer move freely.
Merkel has called Europe "vulnerable" and that the fate of the euro is "directly linked" to resolving the migration crisis.
Juncker cited the European Commission's own data of the 3 billion euro annual cost, also saying that according to independent estimates, the closure of the bridge between Denmark and Sweden could cost 300 million euros a year in lost business.
Several national governments have used emergency powers under the Schengen treaty to reinstate border checks with EU neighbors in response to chaotic treks by about 1 million people seeking asylum last year, most of whom landed in Greece.
Those movements have made a nonsense of EU rules, known as the Dublin system, under which people must claim asylum and be accommodated in the first EU state they enter. In effect, most of last year's arrivals ended up in Germany.
Since last year, the Commission has been working on reforms to be proposed by March to spread responsibility more evenly, rather than leave Greece and Italy with the notional legal obligation to accommodate nearly every asylum seeker in Europe.
One idea, favored by Germany but which faces fierce resistance from many member states not yet affected by the crisis, is to relocate people around the bloc according to a quota system based on population and national wealth.