Uefa's 53 members back governing body's Sion stance
Uefa's 53 national member associations have given their unanimous backing to the governing body over its decision to expel Sion from the Europa League.
Celtic were reinstated to the group stages when Sion were thrown out for naming five ineligible players in their play-off win over Neil Lennon's side.
The Swiss side have since been to their country's courts to argue their case.
But Uefa's members say a club refusing to accept the rules of the competition "should not participate in it".
Sion's legal challenge to Uefa's ruling is being viewed as a threat to its authority and that of the world governing body, Fifa.
Uefa's emergency panel last Tuesday dismissed a ruling from the district court in Vaud that Sion should be allowed back in the competition, from which they were thrown out on 2 September.
Two days later the same court ruled that the opening round of Europa League Group I fixtures, including a 2-0 defeat for Celtic at Atletico Madrid, were invalid.
But in a statement released on Wednesday called "Declaration of the 53 Uefa member associations regarding the FC Sion case", the members have hit back at the Swiss club.
The statement said: "The 53 national associations of Uefa have today unanimously declared their support for Uefa president Michel Platini, the Uefa executive committee, the Uefa general secretary, the Uefa disciplinary bodies and the Uefa administration for their determination to uphold the statutes and regulations of football.
"The European national associations call upon both Fifa and the Swiss FA to urgently take concrete steps to uphold the statutes and regulations of Fifa, as Uefa has done.
"The independent sports justice system is the best guarantor of equality and fairness for all participants in sports.
"The European national associations declare that any member of the football family which refuses to accept the rules of the competition should not participate in it."
After Uefa's disciplinary body threw out Sion's initial appeal last week, the club announced it would initially seek compensation from Uefa of more than 4m euros and potentially tens of millions in the long term.
"Uefa believes that it rules the world," a Sion spokesman said at the time.