Olympic 100m hurdles champion Brianna McNeal has been provisionally suspended from athletics after being charged with breaching anti-doping rules.
The American is accused of "tampering within the results management process", the Athletics Integrity Unit said.
McNeal, 29, won gold at the 2016 Rio Olympics and was also world champion three years earlier.
She missed the 2017 World Championships while serving a one-year ban for missing three drug tests.
Tampering or attempted tampering with any part of doping control carries a ban of up to four years if proved.
As McNeal has served a ban in the past, if found guilty she could face a ban of up to eight years.
She was disqualified from the 100m hurdles at the 2019 worlds in Doha after a false start in qualification.