Barcelona have reacted angrily after the Court of Arbitration for Sport (CAS) upheld FIFA's decision to punish the club with a ban for two consecutive transfer windows.
Barca then took their appeal to CAS, but that has also been rejected, meaning the club will not be able to sign any players in 2015.
A statement on the CAS website read: "The Court of Arbitration for Sport (CAS) has dismissed the appeal filed by FC Barcelona against the Federation Internationale de Football Association (FIFA) regarding the decision issued by the FIFA Appeals Committee on 19 August 2014.
"In such decision, the Spanish football club was sanctioned with a transfer ban for two periods, a fine of CHF 450,000 and a reprimand after it was found to have infringed the FIFA regulations with respect to the registration of a number of minor players.
"In appealing to the CAS, FC Barcelona sought to annul the FIFA decision. The parties agreed to an expedited procedure and a hearing was held at the CAS headquarters on 5 December 2014 where the CAS Panel in charge of the matter (Prof. Petros Mavroidis, Greece, (President), Mr Efraim Barak, Israel, and Prof. Ulrich Haas, Germany) heard the parties, their representatives and their witnesses.
"The panel found in particular that FC Barcelona had breached the rules regarding the protection of minors and the registration of minors attending football academies (articles 19 and 19bis of the FIFA Regulations on the Status and Transfer of Players). Accordingly, the FIFA decision is confirmed in full and the sanction remains in force.
"In view of the need to issue a decision before the opening of the next transfer window, the Panel has issued its decision without the grounds. The full Arbitral Award, with the reasons for the Panel's decision, will be issued as soon as possible."
FIFA later issued a statement saying "CAS has shown clear and strong support for FIFA's efforts to protect underage players," but Barcelona insisted the punishment was "completely disproportionate."
A statement on the club's official website read: "FC Barcelona wishes to state, with all due respect for the sports authorities, that it totally disagrees with the verdict of the Court of Arbitration for Sport (CAS) announced today to confirm the sanction originally imposed by FIFA as a consequence of the alleged breach of regulations on the international transfer of minor footballers.
"The club has made it clear to the FIFA Disciplinary Commission, the FIFA Appeals Commission and the CAS itself that it understands and supports the policy on the protection of minors and the concern for the protection of their development and education.
"This is confirmed by how they club has acted throughout its history, setting an example around the world for the way its young footballers are schooled and educated, and the work that is done on their development. FC Barcelona's youth structure has enabled hundreds of young players to achieve their dreams and receive a decent upbringing.
"The errors that the club might have committed, and which have been recognised and argued before the corresponding authorities are, in all cases, of an administrative nature and to a large extent have been caused by the existing conflict between the FIFA regulations and Spanish legislation, along with the club's conviction that it was acting correctly.
"Therefore, FC Barcelona considers the sanction to be completely disproportionate as it supposes an excessive punishment for the club, when considering its trajectory and the circumstances of this specific case."
Barca had protected themselves against such a ruling in the summer, when they signed a host of new players.
They are also permitted to renew players' contracts, such as Dani Alves, and can bring the likes of Denis Suarez and Gerard Deulofeu, both on loan at Sevilla, back into their squad.