Mercedes-Benz and three of its dealers have been fined £2.6m after an investigation by the Office of Fair Trading (OFT) into market rigging.
The case was focused on the distribution of Mercedes-Benz trucks and vans in the north of England and parts of Wales and Scotland between 2008 and 2010.
The Daimler-owned company and vehicle dealers Ciceley, Road Range and Enza admitted infringing competition law.
Mercedes-Benz was fined £1.5m and Ciceley received a £659,675 penalty, while Enza Motors was fined £347,000 and Road Range was hit with a £115,000 penalty.
A further dealer, Northside, avoided a fine because it was the first company to provide evidence of collusion after the start of the investigation.
The watchdog said the infringements were in relation to market sharing, price co-ordination and the exchange of commercially sensitive information.
OFT's senior director of cartels, Ali Nikpay, said the companies' admissions resulted in their penalty being reduced by 15%.
He added: "These cases send a clear signal that the OFT will take firm action against companies that collude to deny customers the benefit of fair competition regardless of the size of the firms involved or geographic scope of the investigation."
A Mercedes-Benz UK spokesman said it had reached a settlement with the OFT for one infringement of competition law relating to a meeting held in 2009.
"Mercedes-Benz regrets the incident and has learned a lot from it.
"The company has strengthened its internal controls, and every member of staff participates in comprehensive and ongoing integrity training programmes," he said.