Barcelona have also been fined 450,000 Swiss francs (£297,000) after being punished for "breaches relating to the international transfer and registration of players under the age of 18."
A FIFA investigation found Barcelona and the Spanish Football Federation were guilty of a "serious" infringement of rules regarding the signing of youth players in the case of 10 members of their academy. As part of the decision they have been given 90 days to rectify the situations of all the minor players involved.
The club have already confirmed they will appeal against the decision at the Court of Arbitration for Sport, the last avenue of legal recourse.
Barcelona's club statement said: "Following the resolution announced today by the FIFA Appeals Committee on violations of regulations regarding the transfer and registration of children aged under 18 years, FC Barcelona announces that it shall continue defending its interests before the highest sporting authority, in this case the Court of Arbitration for Sport (CAS).
"FC Barcelona may not in any way share a resolution that is an affront to the spirit of our Masia, a world renowned example of academic, human and sporting education."
Barca were initially banned in March from making any new signings for two transfer windows but appealed against the decision, allowing them to strengthen their squad this summer.
A deal for Luis Suarez, worth between £65m-£75m, was permitted along with the captures of Croatian midfielder Ivan Rakitic, Arsenal defender Thomas Vermaelen, Valencia centre-back Jeremy Mathieu and two goalkeepers in Marc-Andre ter Stegen and Claudio Bravo.
However, assuming that the CAS do not overturn the ban, Barcelona will now be prevented from making any new signings in the January transfer window and next summer as well.
A FIFA statement read: "The FIFA Appeal Committee has decided to reject the appeals lodged by Spanish club FC Barcelona and the Real Federación Española de Fútbol (RFEF) and to confirm in their entirety the decisions rendered by the FIFA Disciplinary Committee in the respective cases relating to the protection of minors.
"As such, FC Barcelona is to serve a transfer ban which will see the club prevented from registering any players at both national and international level for two complete and consecutive transfer periods, starting with the next registration period (January 2015) given that the appeal of the club had been granted suspensive effect by the chairman of the FIFA Appeal Committee.
"FC Barcelona has also been ordered to pay a fine of CHF 450,000 and been given a period of 90 days from today in which to regularise the situation of all minor players concerned. Meanwhile, the RFEF has been ordered to pay a fine of CHF 500,000 and granted a period of one year in which to regularise their regulatory framework and existing system concerning the international transfer of minors in football.
"The terms of the decisions taken by the FIFA Appeal Committee were communicated to FC Barcelona and the RFEF today."
In addition, the Spanish Football Federation also lost its appeal against a fine of 500,000 Swiss francs (£330,000).
"The RFEF has been ordered to pay a fine of CHF 500,000 and granted a period of one year in which to regularise their regulatory framework and existing system concerning the international transfer of minors in football," FIFA's statement said.
This could be a hugely significant decision. Although Barcelona have taken the opportunity to bolster their squad significantly this summer, taking the sting out of the punishment, FIFA's decision to stand by the ban means Real Madrid - never shy of making superstar signings - can try and accelerate away from their rivals in 2015 for good. Not only that, but Atletico Madrid will feel they can strengthen their relative position too with a few canny additions.
This also removes one of the big players from the transfer market, increasing opportunities for clubs from England to land their big targets throughout 2015. If the CAS doesn't overturn the decision then today's news will have far-reaching implications for the transfer market.
VIEW FROM SPAIN
Iganzio Ruiz of Eurosport Spain: "FC Barcelona and people in general expected some reduction to the ban - so it's unsurprising that Barça have just officially announced that they will appeal to the CAS. They will be confident of some good news down that route - just as they were with Suarez. In the meantime, however, there are no further worries for them: the ban starts in January, and they have already signed a lot of players this summer."
- Sports & Recreation
- FC Barcelona
- Spanish Football Federation