Steel workers have attacked ArcelorMittal's Luxembourg headquarters, throwing objects at the building and trying to break down the front door, to protest against temporary layoffs.
Some 2,000 workers from Belgium and France are protesting, the police say. Some of the demonstrators have set off smoke bombs and hurled projectiles during the company's shareholder meeting.
ArcelorMittal chief executive Lakshmi Mittal says steel output has halved as demand slumps but the freeze is temporary.
Belgian unions warned yesterday that tensions were high because the company won't give firm details on restarting shuttered plants.