The Riva family, owners of the ageing Ilva plant in Taranto in southern Italy Europe's biggest steel mill, are suspected of illegal association for alleged crimes against the environment.
The sum is the equivalent of what the family should have invested to counter the environmental impact at the plant, which employs thousands of people and was once a symbol of Italian industry.
The investigation into an environmental disaster at the plant began in July 2012 with the arrest of Emilio Riva, who was placed under house arrest. In November, the police carried out more raids and Riva's son, Fabio, escaped by fleeing to London.
The Ilva plant's future has been contested for months, with prosecutors calling for it to be closed and many of the workers asking that it remain open.
Ilva represents 40 percent of Italy's steel production.