Swiss-based industrial giant ABB is among six companies fined a total of €67.6 million (SFr102.2 million) by the European Commission for anti-competitive practices.
The Commission said on Wednesday that ABB, Japan's Toshiba and other firms had taken part in a "gentleman's agreement" not to compete with each other in the European and Japanese power transformer markets.
ABB was hit with a €33.8 million fine. Germany's Siemens had its fine waived because it blew the whistle on the cartel.
"The Commission has now put an end to this rip-off by the self-appointed gentlemen," European Union Competition Commissioner Neelie Kroes said in a statement.
"The Commission will not hesitate to increase fines for repeat offenders until they have learned the lesson that cartels do not pay," Kroes added.
Power transformers are used to modify the voltage in electricity transmission networks.
The fine for ABB was increased by 50 per cent because it had previously taken part in a similar infringement, the Commission said.
The Commission imposed a joint total fine of €16.5 million on French firms Areva and Alstom, which also has facilities in Switzerland. It fined Japan's Hitachi €2.4 million and Fuji Electric €1.7 million for their roles in the cartel.
swissinfo.ch and agencies