Cemex is considering an appeal after it was hit with a massive fine after cement dust escaped from a silo at its Rugby production plant.
Judges at Warwick Crown Court fined the company UK£400,000 after it admitted pollution charges following an incident in October 2005.
The firm was also ordered to pay almost UK£12,500 in costs by the court.
Cemex had pleaded guilty to the leak at the Magistrates’ Court in Rugby but magistrates referred the case to the Warwick Crown Court for sentencing because they felt the maximum £20,000 fine it could impose was insufficient.
The court heard how dust escaped through a faulty door on the side of a silo and covered homes and cars as far as three miles away from the plant.
A passer-by had spotted the damage to the silo and warned the company but it failed to carry out full repairs until the following day.
The Environment Agency welcomed the severity of the fine and claimed it would ensure Cemex would improve its maintenance regime.
A Cemex spokeswoman commented: "We regret the incident but feel that the level of fine is excessive and disproportionate."