The OFT has stated that by telling race tracks when to stage meets, how much to pay winners, and by monopolizing race data, the sport's organisers may be breaking legal conditions.
The two bodies under the limelight - The Jockey Club and the 10-year-old British Horseracing Board - have been given 11 weeks to respond to the OFT's claims.
If they fail to convince the UK regulator, the rules will be outlawed pending an appeal process.
The ruling may allow courses to hold more meetings and result in lower fees to reproduce race information. Bookmakers reportedly paid about £86 million ($133m) in 2002-2003 for the rights to publish data such as which horses are running.
Under existing rules, tracks cannot stage races if a meeting is taking place within 50 miles (80 kilometers). Course owners have to pay out a minimum amount of prize money and are limited to how many races they hold per meet.
Commented BHB chief executive Greg Nichols: "The announcement suggests that the OFT has fundamentally misunderstood how and why British racing operates as it does. There is strong competition."
The BHB raises funds by selling racecard data although bookmakers have complained about the cost of the information.
