Five top modelling agencies and a trade association have been fined a total of £1.5m for colluding to fix charges.
The Competition and Markets Authority (CMA) said they regularly and systematically exchanged information and discussed prices.
The biggest fine was given to the Storm agency, which uses models like Alexa Chung and Cara Delevingne.
However, the CMA stressed that big name “top models” were not involved in the price-fixing.
It said the five agencies got together regularly to agree on a minimum level of prices – which is against the law.
The CMA also accused the Association of Model Agents (AMA), the trade association, of sending round emails to its members telling them to keep prices high.
The CMA investigation looked at a wide range of modelling assignments, from small magazine shoots to big advertising campaigns.
It said that the customers affected included well-known High Street chains and online fashion retailers.
“Strong competition benefits consumers, the economy and society,” said the CMA’s John Wotton.
“In this case the agencies and the AMA colluded with each other over their approach to pricing and, in some instances, the agencies agreed to fix minimum prices.”
Storm Model Management was fined £491,000; Models One was fined £394,000, and FM Models has been told to pay £251,000, although it has since gone bust.
Smaller fines were given to Viva Model Management and Premier Model Management.
The AMA was fined £2,500.