The Swiss Super League side were thrown out of the competition for fielding ineligible players in their play-off tie against Celtic, who were installed in Group I in their place.
It emerged on Friday that Sion had produced a new court order from the Tribunal Cantonal de Vaud demanding a response from UEFA by noon on Monday outlining "the measures it has taken to integrate Sion in the Europa League".
CAS confirmed its competence to deal with the case yesterday, which relates to alleged breaches of a transfer embargo by Sion which was imposed on the club for breaching rules in the signing of Egyptian goalkeeper Essam El Hadary in 2008.
In the statement, UEFA reported that CAS felt Sion had been guilty of "clear abuse of CAS procedures" by seeking to refer the case to other courts and European football's governing body accused them in their statement of "repeated attempts to obstruct justice".
The statement added: "UEFA recalls that delaying a conclusion in this case will present a major prejudice to the whole UEFA Europa League, especially the other clubs in the competition.
"UEFA therefore once again urges FC Sion to come quickly to CAS, as it promised to when it entered the UEFA Europa League, in the same way as every other club."