Barca's appeal against a transfer ban imposed by FIFA was rejected by the Court of Arbitration for Sport (CAS) on Tuesday.
The Liga club were handed the sanction in April after irregularities were found in their dealings at youth level.
FIFA suspended the punishment pending an initial appeal to the governing body, which was dismissed, with the Catalan club subsequently opting to the take the case to CAS.
Uruguay striker Luis Suarez has been among those to join Barca while the embargo has been on hold, making the switch from Liverpool for a fee in the region of €80 million.
However, Barca will now be unable to add to their squad until 2016 after CAS determined FIFA's original decision to ban them from making signings for two transfer windows should stand.
Barca expressed "its total disagreement with the resolution" and revealed their intention to explore their legal options, before president Bartomeu released a statement of his own to express his criticism of the decision.
"A great injustice has been committed today: an injustice for Barca, for all the children and parents affected by this decision, for all the club members and for football in general," he said.
"We have always made it clear that we consider FIFA’s sanction to be disproportionate. This judgement by CAS, which ratifies FIFA's decision, is not good for us and defies all sporting logic.
"FIFA and its president have to be an organisation which protects the footballing world and decisions like this distance it from this objective. We do not feel supported or protected by those people who should be doing this.
"The strict letter of the law has been observed, rather than the spirit in which it was written and a precedent that is not good for the game in general has been created - one which has attempted to tarnish the good name of our club.
"I wish to announce that Barca, with myself in the lead, will fight to change this regulation and improve it.
"I hope that FIFA will show sufficient common sense to re-write this regulation and that no other club will have to suffer this injustice. Despite everything, I can guarantee our members that this sanction does not endanger the sporting project at La Masia.
"And I remain optimistic. On the one hand, we have a squad which offers sufficient guarantees to cover any possible needs of the first team and on the other, we have to bear in mind that the signings we made last summer to strengthen the squad were made with the possibility of this sanction in mind and to allow us to contend for all the possible titles we are competing for until this sanction is over."
