STORY: U.S. swimming star Michael Phelps told a congressional panel on Tuesday that anti-doping measures concerning Chinese swimmers 'have fallen short' ahead of the Paris Olympics.

Phelps was joined by fellow gold medalist Allison Schmitt as well as the CEO of the US Anti-Doping Agency Travis Tygart.

They all testified to lawmakers they've lost faith in the World Anti-Doping Agency (WADA) over its lack of reform.

Congresswoman Cathy Rodgers asked Phelps what stands in the way of competitions being free and fair of illegal drugs:

"I think a lack of level playing fields, lack of rule following across the board, right. I mean, you heard the schedule that we have to give every hour of every single day. They have to know exactly where we are. USADA (United States Anti-Doping Agency) knows exactly where we are. And again, we are okay with that. If everybody else is doing that, then that's what I want. I want to be able to stand up to the block with somebody next to me and be like 'All right, cool, this is me versus you,' It's not me versus you and seven other drugs."

While neither will compete in Paris, Phelps, with 28 medals to his name, is the most-decorated Olympian of all time, and Schmitt won 10 medals over four games.

WADA confirmed that Chinese swimmers tested positive for a banned substance, leading to calls for accountability and fair competition.

WADA declined to testify at the Tuesday hearing, citing the focus on the Chinese swimmers' case.

Travis Tygart said WADA should have taken immediate action:

"They should have immediately provisionally suspended the athletes, take them off the playing field. That's mandatory under the rules. That was not done. WADA (World Anti-Doping Agency) has the appeal right when anti-doping organizations like China in this case failed to impose a mandatory provisional suspension. WADA should have immediately appealed that. Like they did in the Russian figure skater case, if you remember. She was not provisionally suspended by Russia, surprise, and they appealed that."

Lawmakers of both parties slammed WADA's handling of the situation - calling it unacceptable.

Phelps highlighted the impact on his friends affected by the case, and criticized WADA for its inconsistent enforcement of policies globally.