The world of Jean-Pierre and Luc Dardenne — a zone of factories, housing projects and modest suburban developments in and around the industrial Belgian cities of Seraing and Liege — is no place for a movie star. The Dardenne brothers, twice winners of the top prize at Cannes, practice an austere and democratic style of realism. Their working-class heroes and heroines make their way in stark circumstances, their ethical dilemmas and material challenges presented without glamour, or soundtrack music.

‘TWO DAYS, ONE NIGHT’ Rated: PG-13 Opens Friday at Kahala 8

That the newest member of this select, unhappy company is played by Marion Cotillard, an Oscar winner and glossy-magazine icon, makes little difference, apart from the fact that Cotillard’s performance is as fine a piece of screen acting as you will ever see. It would be facile to say that in "Two Days, One Night," she disappears into the role of Sandra Bya, a working mother fighting to save her job at a small company that makes solar panels.

Her shoulders slumped, her eyes weary, her gait heavy, Cotillard moves past naturalism into something impossible to doubt and hard to describe. Sandra is an ordinary person in mundane circumstances, but her story, plainly and deliberately told, is suspenseful, sobering and, in the original, fear-of-God sense of the word, tremendous.

After a medical leave during which she was treated for depression, Sandra has returned to work, only to discover her position is in danger of disappearing. The company has offered her co-workers a choice: If she is laid off, all of them will receive a 1,000 euro ($1,200) bonus; if they give up the bonuses, she can keep her job.

A vote has already been held among the 16 members of Sandra’s work team, but her boss agrees to a second ballot. This gives Sandra a weekend — two days and one night — to persuade a majority of her colleagues to sacrifice on her behalf.

Sandra and her husband, Manu (Fabrizio Rongione), live with their two children in a clean, well-appointed town house, a big, hard-won step up from the "social housing" where they used to live. The thought of going back is especially galling to Manu, who works in the kitchen of a chain restaurant and who pushes his wife to make her case. Anxious, frequently tearful and quick to reach for a Xanax, Sandra would rather curl up in bed than endure the humiliation of begging for the pity of her peers.

The film consists almost entirely of encounters between Sandra and the people who have the power to decide her fate. The key to the movie — what makes it moving as well as grueling — is that the Dardennes refuse to skip or cut away from a single meeting. Like Sandra, the audience must absorb the emotional impact of each conversation. A man bursts into tears. A fistfight breaks out. A marriage comes undone. A blunt refusal is followed by an offer of orange juice.

Work, for Sandra and her fellow citizens of the Dardenne Republic, is an irreplaceable source of meaning, identity and happiness. "Two Days, One Night" is about the erosion of all of those values, and also about the waning of solidarity in the modern economy. In the past, the quality of life that workers like Sandra and Manu enjoy might have been secured through collective struggle. Now, the film suggests, it is maintained through individual competition among the workers themselves.

This is a grim reality — but the Dardennes are too committed to the dignity of their characters to set themselves up as merchants of despair. "Two Days, One Night" does not paint a pretty picture of today’s world. Partly for that reason — and partly because of the gravity and grace of its star — it’s a beautiful movie.