BEVA spokesman Henry Tremaine, B Vet Med MPhil Cert ES Dip ECVS MRCVS
Anger is growing around the globe at the FEI's decision to allow small amounts of certain therapeutic drugs in a horse's system in competition, including the powerful anti-inflammatory phenylbutazone.
The latest group to voice its concerns is the British Equine Veterinary Association.
The association described the introduction of the so-called "progressive list" of medications "to be an extremely retrograde step for equine welfare".
"This decision obscures the distinction between therapy and subjecting unsound horses to the stresses of competition," spokesman Henry Tremaine said.
"Furthermore, we have grave concerns that horses competing whilst under treatment with pain-relieving medicines, are at an increased risk of musculoskeletal lesions progressing to catastrophic injuries," he said.
"We see this announcement as a backward step for the development of equestrian sport that is contrary to the public aspiration of drug-free competition.
"We would strongly encourage a rational review of the available evidence and if necessary new research to try and formulate a more scientific basis for these regulations."
The FEI general assembly's decision to relax the rules in respect of half a dozen commonly used drugs has completely overshadowed the adoption of its Clean Sport programme, which it hailed last week as a landmark decision.
Leading equestrian nations represented at the general assembly opposed the adoption of the progressive list, which was passed in a close vote, effectively removing the zero-tolerance policy which has been in place for years.
The statement from British organisation follows a letter written to FEI president Princess Haya from senior equine veterinarians around the world, including Dr Leo Jeffcott, former chairman of the FEI Veterinary Committee.
They expressed their grave concern over the introduction of the progressive list, saying it had seriously over-shadowed the clean sport campaign.
"The progressive list, which we understand was seen for the first time by the delegates when they arrived for the assembly, has not been debated sufficiently and we believe a decision has been made that was premature, ill-considered and seriously retrograde."
They argued that use of anti-inflammatories will lead to abuse and the participation of horses in competition that are unfit to compete.
"It also removes the 'level playing field' that has been a crucial and fundamental ethos of the FEI since its foundation.
"We believe the decision must be reconsidered."
The veterinarians said adoption of the progressive list would have "a serious and negative effect on welfare and profound repercussions for equestrian sport".
"National legislation in many European countries prohibits any medication in competition animals. This does not apply in parts of the US where 'permitted levels' are more common.
"A 'controlled restricted' list will surely be unenforceable where it is in conflict with the national laws of a country," the vets pointed out.
The letter was signed by 15 vets, including members and former members of the FEI veterinary committee and Andrew Higgins, the FEI's honorary scientific adviser and former chairman of its Medication Advisory Group.
It has also become clear in recent days that the new policy will put the FEI into conflict with organisers of the renowned World Equestrian Festival at Aachen and at least one major sponsor. They have vowed to run the event according to their own anti-doping policies.
Frank Kemperman, chairman of the managing board of the Aachen-Laurensberger Rennverein e.V. (ALRV), said: "The FEI's decision is a contradiction to our ideal of the sport."
Kemperman, as chairman of the FEI's Dressage Committee, was in Copenhagen last week for the General Assembly and vehemently fought against the new regulations.
On Monday CHIO Aachen organisers said that in the future, the event will continue its straightforward strategy for fair and clean sport.
Deutsche Bank General Manager Michael Mronz said: "We do not want to have unsound or injured horses in our sport. The CHIO Aachen 2010 will not be carried out on the basis of the current FEI regulations, but according to the ethics of clean sport."
The Deutsche Bank, which has been supporting the event for 52 years, has extended its contract with the festival CHIO Aachen for another three years. The bank is also traditional partner and title sponsor of the Deutsche Bank Prize, the dressage competition with the highest prize money in the world.