Workers occupied the Marine Harvest smoked salmon factory in Brittany, north western France, against its closure on Monday of last week.
Over 250 people rallied last Friday and up to 80 workers struck in solidarity at other Marine Harvest sites last week.
Brittany has lost almost 10,000 jobs in a few months. Fury at the cuts has seen a town hall occupied and tens of thousands demonstrating.
The “red bonnet” movement has also attacked motorway cameras and toll booths. They oppose a government planned “ecotax” on road transport that will cost the region three times what is promised in aid.
Much of the left supported the ecotax and opposed the demonstrations as being in the interests of bosses, not workers.
But the New Anticapitalist Party marched on the demonstration behind a banner calling for sackings to be banned. It pointed out that the infrastructure the ecotax will fund would mainly benefit big business.