Frankie Dettori was asked to give up a mount at Newbury because the race was being run for a prize below the Horsemen's Tariff.
Dettori was due to partner the Robert Mills-trained Diamond Vision in the Scope Handicap but was replaced by Jim Crowley.
The jockey is retained by Godolphin, who will not enter runners in below-tariff races.
"I was asked to get off the horse by my bosses because it's under the tariffs." said Dettori.
The Horsemen’s Group represents British racehorse owners, trainers, jockeys, stable staff and thoroughbred breeders.
Its constituent bodies are the Racehorse Owners Association, National Trainers Federation, Professional Jockeys Association, National Association of Stable Staff and Thoroughbred Breeders Association.
They have drawn up the Horsemen’s Tariff as recommended minimum prize-money values for each class of race run at race meetings under the Rules of Racing in Britain.
