The British Horseracing Authority has been urged to drop the case against jockey Robbie Dunne in the Bryony Frost bullying probe.
The Professional Jockeys Association called upon the sport's governing body to act, because they say "a fair hearing is impossible."
Their stance comes after confidential documents were leaked and their content appeared in the press.
It emerged that Dunne was charged with “conduct prejudicial to the integrity or good reputation" of the sport after a lengthy investigation.
Dunne, whose biggest success came in the 2015 Scottish National riding Wayward Prince, denies the allegations.
In a statement, the PJA said: "The length of time taken in bringing this case to a conclusion is unacceptable.
"Now that material has been leaked to the media, and the information leaked is the charge letter and accompanying documentation that should only have been available to the BHA, Robbie Dunne and his legal advisers, a fair hearing is impossible.
"The matter cannot now be permitted to proceed – and we call upon the BHA to bring this matter to an end, however unsatisfactory that is."
The British Horseracing Authority’s 120-page report, covered by The Sunday Times, is said to contain complaints from Frost about her weighing room colleague's behaviour over several years.
These include Dunne allegedly swearing at her after pulling up after a race and in the weighing room.
Frost first revealed the difficulties she was facing in December after winning the King George VI Chase on Frodon having lodged a complaint with the BHA.
Alongside allegations made by her of threatening and inappropriate behaviour by Dunne, the BHA investigators reveal how “there is a cultural issue in which threatening behaviour is condoned and not reported in the weighing room.”
The BHA has reported itself to the Information Commissioners Office over the data leak. The PJA expects members to abide by a code of conduct, published in May, to ensure the sport welcomes everyone and people are held to account against a set of rules and codes of expected behaviour.
PJA Chief Executive Paul Struthers said: "Any individual subjected to behaviour that might constitute a breach of the rules of racing or the PJA's code of conduct must have the right to pursue a complaint and that right must be respected.
"The PJA has no toleration of bullying and does not, and will not, stand idly by when it becomes aware of such conduct."
