Olympic gold-medal winner Caster Semenya is refusing to submit to the newly implemented track-and-field testosterone regulations.
After winning the 800-meter race Friday at the Diamond League, Semenya told reporters "hell no" when asked about taking hormone-reducing medications.
Semenya was asked to verify her gender in 2009 after she won gold at the World Athletics Championships.
Since that victory, Semenya has won two Olympic gold medals in the 800 meters in 2012 and 2016.
Last year, the International Association of Athletics Federations implemented a new eligibility rule requiring female runners who produce higher levels of testosterone to take medications that will lower their levels.
Semenya appealed the ruling, but the Court of Arbitration for Sport voted by majority in favor of the IAAF testing.
"It is not fair. I just want to run naturally, the way I was born," Semenya said in a statement about the decision. "I am Mokgadi Caster Semenya. I am a woman and I am fast."
The new rules will go into effect on May 8, putting Semenya's racing career in jeopardy. The South African star has won 30 consecutive races dating back to 2015 after her triumph Friday.