Since the World Anti-Doping Agency first came under scrutiny this spring for its handling of positive tests for banned substances by nearly two dozen Chinese swimmers, the United States has been the agency’s chief critic.

Congress has threatened to cut funding for the agency, which is known as WADA. The Justice Department and F.B.I. have opened criminal investigations into how the tests were handled. And the head of the United States Anti-Doping Agency and American swimmers have raised doubts about whether WADA can be trusted to do its job.

On Wednesday, WADA launched its latest counterattack on the Americans, accusing the United States Anti-Doping Agency, known as USADA, of doing the same thing it has accused WADA of: failing to strictly follow the rules when an athlete tests positive for a banned drug.

In a lengthy statement, WADA said that USADA had gone against the global antidoping code a decade ago by allowing athletes who had tested positive because of food contamination to continue competing.

WADA acknowledged a wrinkle in the case — that the athletes in question were allowed to keep competing so they could work undercover to help authorities with a criminal investigation — but said it did not matter because the U.S. agency was still bound to follow the rules and had failed to get WADA’s approval.

“In one case, an elite level athlete, who competed at Olympic qualifier and international events in the United States, admitted to taking steroids and EPO yet was permitted to continue competing all the way up to retirement,” WADA said, referring to two categories of banned drugs. “Their case was never published, results never disqualified, prize money never returned and no suspension ever served. The athlete was allowed to line up against their unknowing competitors as if they had never cheated.”