Hayley Turner is to face a British Horseracing Authority inquiry for a breach of betting rules.
British flat racing's most successful female jockey is alleged to have placed 164 bets over an 18-month period.
Chief executive of the Professional Jockeys Association Paul Struthers said in a statement: "Following her retirement from the saddle in November 2015, Hayley opened an online betting account in her name registered to her home address, the first ever betting account she had opened.
"Even though she was officially retired, Hayley subsequently took part in a number of one-off, invitational events and had some warm-up rides to prepare for them, and held a licence from the BHA enabling her to take part in those events.
"It was only this summer that Hayley decided to return to race-riding more fully in France.
"Even though Hayley no longer saw herself as a jockey, and placed no bets whilst actively riding, she did place bets whilst holding a licence, which technically placed her in breach of the rules of racing, something Hayley entirely accepts.
"There were a total of 164 such bets over a period of approximately 18 months, with a median average stake of £10 and a mean average stake of £18.62, which generated a total profit of £160."