The founder of the L214 animal rights group, Sébastien Arsac, and another member face charges of trespassing and invasion of privacy for breaking into the Guy Harang abattoir in Houdan, near Paris, last December and placing hidden cameras to film the way the pigs were stunned before being bled.
But one of the cameras fell of and the pair were arrested when they came to collect them.
The group, which campaigns in favour of vegetarianism and against animal cruelty, has since published video showing the pigs panicking and suffering convulsion attacks as they are lowered into the pit where they are to be stunned by carbon dioxide.
The UN's Food and Agriculture Organisation points out that "the acceptability of this method on welfare grounds has been questioned" and that it may be stressful for some kinds of pigs.
L214 has started a petition to ban CO2 stunning in France and its members joined amarch in Paris on Saturday calling for abbatoirs to be closed down.
There were similar demonstrations in 20 other cities around the world.
Farmers' support abattoir
The abattoir's boss, Vincent Harang, has said that its CO2 machine complies with legal requirements.
Local farmers planned to demonstrate to support him at the court on Monday.
The slaughterhouse employs 90 people and kills 2,500 pigs every week.
Since 2013 L214 has published a number of videos exposing alleged cruelty in French abattoirs, leading to the creation of a parliamentary inquiry.
It drew up 65 recommendations, including the installation of CCTV cameras, a proposal endorsed by France’s parliament in January.
The move is planned to be rolled out in January next year, following an experimental phase this year.