Barcelona have been given a transfer ban for two consecutive windows and fined 450,000 Swiss francs ($509,400) for breaching rules on the international transfer of foreign under-18 players, FIFA said on Wednesday.
The Spanish federation (RFEF) was fined 500,000 Swiss francs after soccer's world governing body found it had also breached rules on the transfer of minors, FIFA added in a statement.
The decision by FIFA's disciplinary committee means the Spanish champions will be barred from taking part in the transfer market until the end of the 2014/15 season.
FIFA described the infringements as "serious" and said Barcelona had been given 90 days to regularise the situation of the players involved.
The RFEF was given one year to "regularise their regulatory framework and existing system concerning the international transfer of minors in football."
FIFA said: "The RFEF and FC Barcelona were found to have violated several provisions concerning the international transfer and first registration of non-Spanish minors with the club."
"Barcelona has been found to be in breach of... the regulations in the case of ten minor players and to have committed several other concurrent infringements in the context of other players," it added.
FIFA said the sanctions referred to transfers made between 2009 and 2013. "The Disciplinary Committee underlined that FIFA takes the protection of minors in football very seriously," said soccer's world governing body.
"The protection of minors is one of the key principles included in the agreement concluded between FIFA, (European governing body) UEFA and the European Commission in 2001.
"The disciplinary committee acknowledged that young football players are vulnerable to exploitation and abuse in a foreign country without the proper controls.
"This particular fact makes the protection of minors in football by the sport's governing bodies, especially by FIFA, even more important."
FIFA's rules ban the international transfer of under-18 players except under limited circumstances which must be evaluated by the its Players' Status Committee.
"The protection of minors in the context of international transfers is an important social and legal issue that concerns all stakeholders in football," it said.
"Above all, the disciplinary committee highlighted that while international transfers might, in specific cases, be favourable to a young player's sporting career, they are very likely to be contrary to the best interests of the player as a minor."
FIFA said its investigations were conducted with the help of its electronic transfer matching system.