Five UK firms are among 30 companies to have been fined a total of 314.7m euros (£211.5m; $399.4m) for running a copper fittings cartel between 1988 and 2004.
Tomkins, Delta, IMI, Advanced Fluid Connections (AFC) and Flowflex were among those fined by the European Commission for price-fixing.
The cartel influenced prices for copper fittings used with tubes for plumbing, heating and sanitation.
Tomkins was fined £3.6m, Delta £19m, IMI £32.5m and AFC £12.16m.
However, the Commission said that IMI’s penalty had been reduced as it had provided information to investigators.
Flowflex faced the smallest penalty of all the companies, with a fine of £907,736.
The Commission increased the fines for AFC, Delta, Aalberts of the Netherlands and France’s Legris for continuing to operate the cartel after its investigation had begun.
The Commission also said that it lifted the fine for AFC by a further 50% as punishment for providing misleading information.
“We will not only punish firms severely for cartel behaviour, but also increase the fines for flagrantly continuing after a Commission dawn raid and for providing wrong or misleading information,” said Competition Commissioner Neelie Kroes.
One firm, Mueller – which was originally fined £6.9m – eventually received full immunity as it was the first company to come forward with information about the cartel.