France has 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 lodge an official complaint with its neighbour.
The BBC reports Italy has angered France by giving 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''.
Trains are 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.
Italy and other European countries are increasingly concerned about migration from north Africa following political turmoil in the region.
Earlier this month, Italy and France agreed to hold sea and air patrols to try to prevent an influx of people from Tunisia, Egypt and Libya.