Sion have announced they have filed a complaint against UEFA with the European Commission after the club was thrown out of the Europa League when they were found guilty of fielding ineligible players.
The Swiss club were excluded on September 2 with SPL side Celtic taking their place in the group stages despite having lost the play-offs between the two teams.
UEFA have since rejected numerous attempts by the club to regain their place via the Swiss civil court in the canton of Vaud, insisting the Court of Arbitration for Sport is the only authority with jurisdiction over the matter with the hearing set for November 24.
Sion's complaint, which was filed jointly with some of its players, claims UEFA contravened rules including the "right of access to an independent and impartial judge", unjustified restriction of competition and the free movement of workers under the EU-Swiss treaty.
Sion president Christian Constantin said in a statement on the club's website: "Two Swiss courts have already ruled in our favour but UEFA continue to openly violate both court decisions and insist that the CAS have the final word.
"Therefore, as others before us, we were compelled to bring this matter before EU justice."
Sion are calling for UEFA to be fined up to 10% of their annual turnover for "a flagrant and deliberate violation of formal commitments entered into in 2001".
They will be represented by Jean Louis Dupont who previously acted for Belgian Jean-Marc Bosman after his club FC Liege had refused his transfer to Dunkirk.
The European Community's court found in Bosman's favour as it ruled UEFA's rules contradicted an EU treaty on the free movement of people.
Sion's action comes days after UEFA invited the club to a consultation meeting to consider their possible re-integration into the Europa League.
UEFA have already held talks with Celtic and the other teams in Group I over the effects on fixtures should the Swiss club be reinstated.
UEFA had already made contingency plans for Sion's readmission.
The first option would annul the group fixtures already played between Celtic, Udinese, Atletico Madrid and Rennes and start a new five-team group with teams playing each other once.
The second option would see Sion join Group I as it stands and play each team home and away.
UEFA also raised the possibility of Sion moving directly into the last 32 following an undefined play-off.
