The Fifa ban was upheld on Tuesday by the Court of Arbitration for Sport.
Barcelona were punished by Fifa over the signings of players aged under 18. The ban covers two transfer windows and means the team cannot sign a player until January 2016.
"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," said a Barcelona statement.
Barcelona acknowledged that it had made "errors" but said these were "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.
"FC Barcelona considers the sanction to be completely disproportionate" and "excessive".
Barcelona said that when it had the full details of the CAS ruling, it would "study and assess the various legal options available, including the possibility of using the CAS arbitration route to the Swiss Federal Tribunal."