ROME -- Italy's ILVA steel mill, which employs some 12,000 workers, suspended operations on Monday after a magistrate issued seven arrest warrants for managers and ordered the seizure of production for pollution.

ILVA said it will appeal the magistrate's decision, adding that in the meantime this means "the closure of the Taranto plant and of all plants belonging to the group that depend on supplies from Taranto."

It said the magistrate's order made it "impossible to sell its products."

The plant, the biggest in western Europe, has been running at reduced capacity since magistrates ordered parts of it closed in July after an inquiry into damning environmental reports that showed high cancer rates in the area.

The Fiom metalworkers' union, which is part of Italy's biggest trade union Cgil, called on workers at the plant to resist the company's closure order by remaining at their posts and come in on Tuesday as they would do normally.

Union leaders urged Prime Minister Mario Monti to take action, threatening otherwise to hold a protest outside his offices in Rome on Thursday.

The dispute has pitted workers fighting to keep their jobs in a recession economy despite possible health hazards against environmentalists and prosecutors who want the site be cleaned up after decades of heavy pollution.

ILVA on Monday insisted there is "an absolute inconsistency over any excess in mortality that could be ascribed to its industrial activity."

The Environment Ministry has been battling to keep the site open, warning that Italy will lose out to competitors in Europe and China if the mill closes.

Among the seven current and former managers targeted by the arrest warrants was Fabio Riva, vice-president of Riva Group, which controls ILVA. The company's president -- his father Emilio Riva -- has been under house arrest since July.

They are accused of crimes ranging from criminal association to causing an environmental disaster to extortion.

ILVA's president, Bruno Ferrante, and the plant's director, Adolfo Buffo, also are being investigated for failing to abide by judicial decisions.

Copyright Agence France-Presse, 2012