(CNN) Two-time Olympic gold medal winner Caster Semenya is again challenging a ruling requiring her to artificially lower her testosterone to enter competition.

The 28-year-old South African is taking her case to the Federal Supreme Court of Switzerland, she said in a statement, after an appeal was rejected by the Court of Arbitration for Sport earlier this month.

Semenya, the dominant force in women's middle-distance running since the London 2012 Olympics, is hyperandrogenous, meaning she has elevated levels of testosterone.

The rule was announced by the International Association of Athletics Federations (IAAF) in April 2018 targeting women's events between 400 meters and one mile, and immediately derided by the 800 meter champion.

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