Cas has since 1984 been the highest authority in sports law issues. Decisions in Cas, with its headquarters in Lausanne in Switzerland, have only been possible to appeal to the Swiss Supreme Court.
Cas has handled everything from doping bans to who gets to participate in various competitions.
But after Friday's outcome, the door is now opening for athletes, clubs and associations within the EU to instead turn to their respective national courts.
"The judgments handed down by CAS must be able to be subject to effective judicial review", it is stated in the EU Court's opinion.
"National courts or tribunals must have the power to conduct an in-depth judicial review", in order to ensure that CAS's judgments "are compatible with the EU's general order.”
The decision has its background in a dispute between the Belgian football club RFC Seraing and the International Football Association (Fifa).
For almost ten years ago, Fifa punished the club with fines and transfer ban because they sold a part of the ownership of players to a third party. This Seraing opposed and took the case to Belgian court to test whether an authority outside the EU – Switzerland is not a member of the union – really should be the last resort in a legal system for stakeholders in EU countries.
The EU Court's decision means that national courts in EU countries should be able to review Cas judgments.
Cas and Fifa have not yet commented on the EU Court's decision.
