The European Commission has fined 17 bathroom manufacturers a total of €622m (£510m) for price fixing.
The companies, including household names such as Ideal Standard, Roca and Villeroy & Boch, coordinated sales prices for bathroom fixtures and fittings between 1992 and 2004, said the Commission.
The cartel met during meetings of 13 national trade associations in Germany, Austria, Italy, Belgium, France and the Netherlands. Deals included fixing price increases, minimum prices and rebates, as well as exchanging sensitive business information.
The Commission described the firms' practices as "very serious infringements of the EU competition rules", breaking Article 101 of the EU Treaty.
Commission vice president and competition commissioner Joaquín Almunia said: "These 17 companies fixed prices for baths, sinks, taps and other bathroom fittings for 12 years in six countries covering 240m people. The cartel will have harmed businesses such as builders and plumbers and, ultimately, a large number of families. However, as the objective of anti-cartel enforcement is not to precipitate the fall of companies in financial difficulties, the Commission reduced the fines on five companies to a level they could afford.
"Companies should be in no doubt that the Commission will continue its fight on cartels and the level of fines will continue to be such that it should dissuade them from engaging in illegal behaviour in the first place."
US-based firm Masco was granted full immunity as the first company to provide information on the cartel. The largest fine went to American company Ideal Standard (€326m), although responsibility for paying it lies with the former owner of the American Standard Group, which sold its kitchen and bathroom arm to new owners in 2007.
A statement from Ideal Standard said: "Ideal Standard International Holding SARL and its new management team maintain a strict code and comply with competition laws in every country where the company is active. Ideal Standard International runs mandatory training to deter anti-competitive conduct of any kind."
Villeroy & Boch received the second largest fine of €72m, with Finland-based Sanitec following with a fine of €58m. The other firms involved in the cartel were Artweger, Cisal, Dornbracht, Duravit, Duscholux, Hansa, Kludi, Mamoli, RAF, Teorema and Zucchetti.
Villeroy & Boch has said it is convinced the price fixing allegations made against the German company are completely without basis.
Ceo Frank Göring said: "In our view, the argument made by the European Commission with regard to the bathroom ceramics market is absolutely incomprehensible. The European Commission has mixed up two sectors: the bathroom taps and the bathroom ceramics sectors. In bathroom ceramics, only cursory investigations have taken place and, as a result, the decision borders on arbitrariness from our perspective."
Villeroy & Boch has challenged the charges of the Commission from the beginning and has called for the proceedings to be terminated. The company now intends to take legal action.