France has stepped up patrols at a Swiss border crossing point to prevent illegal immigrants from slipping into the country.
Police in the western canton of Vaud say Switzerland is paying the price for lying outside the Schengen area, the world’s largest passport-free zone.
Since late February more than 250 people travelling by train from Italy via Switzerland to France have been turned away by French border guards.
The unilateral move to tighten checks at the small border town of Vallorbe in canton Vaud is being seen in some quarters as proof that Switzerland is isolated in the middle of Europe.
All European Union member states – with the exception of Britain, Ireland and the ten countries which joined in 2004 – are part of Schengen, an accord which removes internal borders.
Switzerland, which is not an EU member, recently signed up to Schengen. But ratification depends on the outcome of a nationwide vote on the treaty in June.
In the meantime, tougher checks at the French border are causing headaches for the authorities in Vallorbe, who are being left to deal with an increasing number of transit rail passengers who lack valid Schengen visas.
Vallorbe, the last stop before the French border, is located on the railway line used by trains shuttling from Venice and Rome via Switzerland to Paris.
A bilateral accord ratified in 1960 gives French and Swiss police the right to carry out border checks on each other’s territories.
It is this treaty which explains the presence of French border-patrol units on the platforms of Vallorbe station. They are permitted to check – and if necessary refuse entry to – anyone attempting to cross into France from Switzerland.
Police in canton Vaud are responsible for ensuring that all those denied entry into France are returned to the country from which they entered Switzerland.
"We have had to put together a plan of action to make sure these people are sent back," says Jean-Christophe Sauterel, police spokesman in canton Vaud.
Cantonal officials say the extra border controls are making heavy demands on their time.
According to Sauterel, 113 officers have so far spent a total of 450 hours dealing with more than 250 people without Schengen visas.
Switzerland is surrounded by Schengen member states and its strategically important location between Italy and France makes it an attractive country of transit for people seeking to move around Europe.
"When leaving the Schengen zone, you have to prove that you have the right papers whenever you arrive at the border of another member country," explains Sauterel.
Some of those stopped at the border in Vallorbe have no papers whatsoever, while others are rejected because they are only in possession of a single-entry Schengen visa which has already been used.
Sauterel’s counterpart in canton Valais, Renato Kalbermatten, says the authorities are doing all they can to stop illegal immigrants from using Switzerland as a transit country.
But he points out that there are limits to what can be done.
"Checks are carried out on all trains operating between Domodossola [in Italy] and Brig [in Switzerland]," says Kalbermatten.
"But if someone has a valid visa for Switzerland, we cannot refuse entry to them solely on the grounds that they don’t have the right Schengen papers."
The Schengen zone is the world’s largest passport-free area.
The following countries are part of Schengen: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Italy, Luxembourg, the Netherlands, Portugal, Spain, Sweden, Iceland and Norway.
Switzerland has signed up to Schengen but adhesion to the treaty depends on the outcome of a nationwide vote in June.
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