In spite of heavy financial sacrifices on the part of the employees and a record profit for their company, the management of the factory, Perrin Industrie, decides on the total closure of the site. Vincent Lindon stars as a union organizer in this brutal account of a workforce betrayed by factory management.

The stage is thus set for a long and grueling fight between labour and management. It is indeed a war, and one of attrition, where both sides wear one another down with their tenaciousness. On the labour side, Laurent (Lindon) and his right-hand gal, Melanie (Mélanie Rover), struggle to keep the strike going as their colleagues begin to lose faith, especially when the company offers them payouts in exchange for their cooperation. And on the management side, there are the French executives, who claim to have no control over the situation, as well as the big bosses over in Germany.

At War captures the tidal swells of solidarity and division that occur within the group of striking workers.