Players' chief Damian Hopley has launched a fierce attack on the decision to hit Sale Sharks prop Karena Wihongi with a four-month ban.
And former England international Hopley, chief executive of the Rugby Players' Association, intends pursuing the matter with what he describes as "relevant national and international bodies."
New Zealand-born Wihongi, 31, was suspended following a positive test for the banned stimulant methylhexaneamine.
He appeared before a Rugby Football Union disciplinary panel earlier this month, having been provisionally suspended by the RFU from playing and training on January 28.
This came after a positive test following an Aviva Premiership game between Sale and Newcastle at Kingston Park three weeks earlier.
Both Wihongi and Sale made representations to the RFU panel that the stimulant entered his system without his knowledge or what the Sharks described in a statement as "without any pre-meditated plan to gain an advantage".
And the punishment, which means Wihongi cannot play again until May 27, has led to Hopley hitting out.
Hopley said: "The RPA fully endorses the fight against doping in all forms of sport and actively promotes strong anti-doping messages to all of our members.
"But we are extremely concerned at the inconsistency concerning the recent punishments handed out to players who have unknowingly taken these contaminated substances containing the stimulant methylhexaneamine.
"The fact that Karena was given the supplement at half-time in a game with the tacit understanding that the substances were certified as clean, seems to have had no impact whatsoever in the sentence that was subsequently passed.
"While we fully accept that all athletes are ultimately responsible for whatever supplements they ingest, the RPA will be taking up this matter with the relevant national and international authorities as we believe this inconsistency and the lack of empathy shown in this case is wholly unacceptable in professional sport."
Wihongi, who is qualified to play for France, joined Sale last year following stints with French clubs Oyonnax and Bourgoin.
The Sharks said: "It was demonstrated to the panel that the stimulant became present via a contaminated product that was available through the club's supplements programme.
"When the product in question was supplied to the club it was issued with a batch test certificate that showed no traces of any banned substance.
"The ingredients of the product had previously been checked and all had been cleared." Under the terms of his ban Wihongi is not able to participate in playing, training, coaching, officiating, selection, team management, administration or promotion of the game.
The club continued: "Sale Sharks would like to place on record our full support for the UK anti-doping testing programme.
"There is no place in sport for drug cheats, and the penalties enforced for those that attempt to gain an advantage by using banned substances are correct and appropriate.
"However, the club are frustrated and disappointed with the verdict given to a player who, without his knowledge, took a product that was wrongly contaminated.
"While the player and the club have the right to appeal the verdict, they will not be doing so.
"Karena Wihongi retains the full support of the club, and we look forward to his return to playing."
Methylhexaneamine is thought to stimulate the central nervous system and increase the body's metabolic rate to give it an energy boost.
It was added to the World Anti-Doping Agency's prohibited list last year after the organisation noticed it appearing in nutritional supplements.
South African rugby union internationals Bjorn Basson and Chiliboy Ralepelle were the most high-profile victims when they tested positive following the Springboks' 23-21 win over Ireland in November.
Ralepelle and Basson are now back in action after a hearing found there was no fault attached to the players surrounding the positive tests.
But Nigerian sprinters Osayemi Oludamola and Samuel Okon were disqualified from the Commonwealth Games in Delhi in October after the substance was detected in their samples, with Oludamola being stripped of her 100 metres gold medal.
And there were also cases involving whole groups of Indian and Australian athletes towards the end of last year, while British shot-putter Rachel Wallader had a year-long ban for a positive test reduced on appeal to four months.
Wallader admitted taking the substance, but only inadvertently, as it was not labelled on a supplement she was using.