Flat glass manufacturer Pilkington has lost its challenge to a €357 million ($445 million) cartel fine after a top EU court said regulators had come up with the correct sanction.

Pilkington, Saint-Gobain and two other companies were hit with a €1.35 billion fine by the European Commission in 2008 for fixing prices and sharing markets over a five-year period starting from 1998.

UK-based Pilkington, acquired by NSG in 2006, challenged the ruling at the Luxembourg-based General Court of the European Union, asking judges to annul the finding and to cut the fine.

Judges at Europe's second-highest court were not convinced by its arguments.

"The Commission did not overstate Pilkington's participation in the cartel and correctly applied EU law in converting that undertaking's turnover (denominated in pounds sterling) into euros," the court said.

"The fine appears proportionate and adequate."

Companies can appeal to the Court of Justice of the European Union, Europe's top tribunal, but only on points of law.