Authorities in France have blocked trains from Italy in an attempt to stop north African migrants from entering the country.
Trains carrying migrants and political activists have been stopped at the border - prompting Italy to launch an official complaint with its neighbour.
Italy has angered France by giving out temporary resident permits to thousands of Tunisian migrants.
The permits allow them to travel freely in many European countries.
The Italian foreign ministry said the French move was "illegitimate and in clear violation of general European principles".
Schengen infringement?
Maurizio Furia, a spokesman for the Italian rail company, said that trains were not being allowed to pass into Menton, France, from the Italian border station of Ventimiglia.
France says migrants have to prove they can support themselves financially and has set up patrols on the Italian border.
But Italy says that France's actions are in violation of the EU's Schengen passport-free travel zone.
"We have given the migrants travel documents, and we gave everything (else) that is needed, and the European Commission recognised that, it has said that Italy is following the Schengen rules," Italian Interior Minister Roberto Maroni said in an interview on Italy's Sky TG24 TV.
Italy and other European countries have been increasingly concerned about migration from north Africa following the political turmoil in the region.
Earlier this month, Italy and France agreed to launch sea and air patrols to try to prevent the influx of thousands of people from Tunisia, Egypt and Libya.
The Schengen Visa has made traveling between its 15 European member countries much easier and less bureaucratic. Traveling on a Schengen Visa means that the visa holder can travel to any (or all) member countries using one single visa, thus avoiding the hassle and expense of obtaining individual visas for each country. This is particularly beneficial for persons who wish to visit several European countries on the same trip. The Schengen visa is a “visitor visa”. It is issued to citizens of countries who are required to obtain a visa before entering Europe.
The purpose of the visit must be leisure, tourism, or business. Upon the issuance of the visa, the visa holder is allowed to enter all member countries and travel freely throughout the Schengen area. It is strongly recommended to plan your journey within the timeframe of the Schengen Visa as extensions can be very difficult to obtain, thus forcing you to leave to stay in compliance with the Schengen rules and regulations. A Schengen visa allows the holder to travel freely within the Schengen countries for a maximum stay of up to 90 days in a 6 month period.
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