Brianna Rollins-McNeal, the 2016 Olympic 100m hurdles champion, has been provisionally suspended after being charged with a doping violation.
The Athletics Integrity Unit (AIU) announced the 29-year-old, who also won gold at the World Championships in Moscow in 2013, has been accused of "tampering with any part of doping control" but did not specify details of the case.
The AIU cited a section in the World Anti-Doping Code that covers conduct which subverts the doping control process.
The code gives one example as altering identification numbers on a doping control form during testing.
Rollins-McNeal served a one-year ban in 2017 after missing three drugs tests, admitting later that she took "full responsibility" for the "mistakes" that led to her failing to update her whereabouts.
Because of her previous suspension, McNeal faces an extended ban of up to eight years if the latest charge against her is upheld.
McNeal won Olympic gold at the 2016 Rio Olympics and is the fourth fastest in history in the event.
Her quest for a second world title ended in Doha last year when she was disqualified for a false start in the heats.