In April, Athletics' governing body announced new regulations affecting women with higher than normal levels of testosterone who compete in track events ranging from the 400 metres up to a mile.
Two-time Olympic gold medallist Semenya is among the athletes who will still be eligible to compete, but only provided testosterone levels are within set limits for a continuous period of at least six months.
The rule will come into force on November 1, but CAS confirmed on Tuesday that Semenya has registered a request to "declare such regulations unlawful" and stop its introduction.
In response, the IAAF released a statement stating they will await further information from CAS, and are "ready to defend the new regulations".
Photo Getty Images. Caption: South African athlete Caster Semenya