It is the latest in a series of trials involving activists trying to help migrants on the move through Europe as France prepares a new immigration law that would speed up deportations of failed asylum-seekers.
Two students, Eleonora Laterza, 27, from Italy and Swiss Bastian Stauffer, 26, along with Theo Buckmaster, a 23-year-old Swiss-Belgian, were detained in April for joining a march of 100 activists escorting some 20 migrants over an Alpine pass.
They were responding to a blockade set up at a nearby mountain pass by several dozen far-right activists from Generation Identitaire (Identity Generation), seeking to keep the migrants out.
If convicted on charges of assisting illicit entry into the country as part of an “organised gang”, the campaigners could face up to 10 years in prison, a fine of up to 750,000 euros ($880,000) and be banned from entering France.
The trial was adjourned Thursday until November 8 to allow the Constitutional Court time to issue a ruling sought by the defence on whether aid to illegal immigrants should be considered a criminal offence.
As the hearing opened, several dozen protesters gathered outside the courthouse in the southeastern city of Gap to stage a “reverse trial” against the government.
At least 12 other activists have been fined or given suspended jail terms since 2015 for helping African migrants arriving from Italy after crossing the Mediterranean from Africa.
The French government argues that tighter controls are needed to check the rise of anti-immigration populists who claim Europe has allowed in too many people seeking a better life.
Polls show the French generally supporting tighter controls.
The bill adopted by the National Assembly in April cuts waiting times for asylum applications reducing it from 12 to six months while facilitating the deportation of “economic” migrants whose applications to stay have been rejected.