In April 2014, FIFA banned the club from buying players for the next two transfer windows following the violation of the FIFA's rules about the transfer of footballers aged under 18. A statement on FIFA's website read "With regard to the case in question, FC Barcelona has been found to be in breach of art. 19 of the Regulations in the case of ten minor players and to have committed several other concurrent infringements in the context of other players, including under Annexe 2 of the Regulations. The Disciplinary Committee regarded the infringements as serious and decided to sanction the club with a transfer ban at both national and international level for two complete and consecutive transfer periods, together with a fine of CHF 450,000. Additionally, the club was granted a period of 90 days in which to regularise the situation of all minor players concerned." FIFA rejected an appeal in August but the pending appeal to the Court of Arbitration for Sport allowed Barcelona to sign players during the summer of 2014.
What was the FIFA  charge that Barcelona violated?
footballers aged under 18