Four of the world's biggest glass manufacturers have been fined a total of 486.9m euros ($717.5m; £348.2m) for illegally co-ordinating price rises.
Pilkington was fined 140m euros for its part in the cartel
The firms are Guardian of the US, Pilkington, which is the UK unit of Nippon Sheet Glass, Saint-Gobain of France and Belgium's Glaverbel.
The European Commission said the firms had raised or stabilised prices in 2004 and 2005 through illicit contacts.
Between them they control 80% of Europe's market for flat glass.
Flat glass is used in products such as windows, glass doors and mirrors.
Glaverbel is a unit of Japan's Asahi Glass and has recently been renamed AGC Flat Glass Europe.
Neelie Kroes, the EU's competition commissioner, said that the EU would "not tolerate companies cheating consumers and business customers by fixing prices and depriving them of the benefits of the single market".
Guardian was fined 148m euros, Pilkington 140m euros and Saint-Gobain 133.9m euros.
Asahi received the smallest fine of 65m euros because it had co-operated with the investigation.
HIGHEST EU FINES (EUROS)
Thyssenkrupp - 480m
Hoffmann-La Roche - 462m
Siemens - 396.6M
Eni - 272.3m
Lafarge - 249.6m
"The important thing is that the fine as a whole is sufficiently deterrent so that no other companies will be tempted to infringe the rules again in the future and I believe we have achieved that aim in this case," Ms Kroes said.
Guardian Industries' group vice president, Peter Walters, said that the firm was "extremely shocked" by the decision.
"We don't believe the facts justify the outcome as it pertains to Guardian," he said.
And a Saint Gobain spokeswoman said the company "took note" of the decision.
She added the firm was braced for an even larger fine from an EU decision on the price of car windows.