Two key bodies which represent US athletes have written to the country’s drug tsar calling for a “truly independent investigation” after it emerged 23 Chinese swimmers were cleared to compete at the Tokyo Games, despite testing positive for a banned substance.
The World Anti-Doping Agency (Wada) said it was "not in a position to disprove" an assertion from the China Anti-Doping Agency (Chinada) that they had unintentionally ingested heart medication trimetazidine (TMZ).
It began an independent review into its handling of the case after an outcry.
Findings of the investigation, led by Swiss prosecutor Eric Cottier, are expected to be delivered within two months.
The US Anti-Doping Agency (Usada) criticised Wada’s appointment of Cottier, calling it a "circle the wagons exercise to protect the system"
And now the Team USA Athletes’ Commission and USA Swimming Athletes’ Advisory Council have jointly written to Dr Rahul Gupta, the director of the US Office of National Drug Control Policy - and the US representative to the Wada Executive Committee - saying they are “extremely concerned” about the case.
In the letter, seen by the BBC, they say the Wada review "appears to be a 'check the box' exercise that will be substantially limited… and thus fail to reveal the whole truth."
They added: “Once again, we are heading into another Olympic and Paralympic Games with serious concerns about whether the playing field is level and the competition fair.
“The decisions made by Wada, the way they were made, and the lack of transparency has undermined our confidence in Wada’s stated mission to 'lead a collaborative worldwide movement for doping-free sport'.
“As athletes, we have to trust Wada to set and enforce standards that will ensure fair play and protect our rights. Wada’s failure to follow its own rules and procedures in the wake of the positive tests of these 23 Chinese athletes has broken this trust.
“Given this, we are asking you… to create and announce a truly independent investigation… perform an audit and ensure that Wada is held accountable to all stakeholders in the handling of this matter; and initiate an independent review that results in greater independence and oversight of Wada and its decisions so that Wada can fulfil the promise it makes to clean athletes and the integrity of the Olympic and Paralympic Games.
“…We believe this is the only way forward.”
Gupta’s role is potentially important as governments fund half of Wada's budget.
International Olympic Committee president Thomas Bach has said he has "full confidence" in Wada.
But Usada chief executive Travis Tygart said Wada and Chinada had "swept these positives under the carpet".
Wada responded by saying those claims were "completely false and defamatory", and had been referred to lawyers.
The Paris Olympics starts on 26 July.
Britain's Olympic champion Adam Peaty and UK Anti-Doping have also called for greater transparency from Wada.
UK Sport chair Katherine Grainger told BBC Sport the issue was "incredibly unsettling for our athletes", a "very disappointing moment for us all" and "should not be happening at this crucial time".