The club confirmed the action in a statement on Friday, less than a week after Pérez secured re-election as Real Madrid president with 65 per cent of the vote. The legal basis is Article 205 of Spain's Penal Code, which covers the crime of slander.
The full statement read: "FC Barcelona informs that today the mandatory conciliation demand prior to filing a complaint for a crime of slander under Article 205 of the Penal Code has been presented against the President of Real Madrid, Mr Florentino Pérez, following the statements made by him at the press conference on May 12 and in an interview with a media outlet the following day."
Barcelona's stated objective is for Pérez to retract "certain statements that he made with knowledge of their falsehood and that are slanderous and offensive to the image and reputation of the Club." Should the demand go unanswered, the club says it will proceed with a formal criminal complaint.
Barcelona's acting president Rafa Yuste had pre-empted the move earlier in the week, framing it in combative terms.
"He has resorted to infamy to destabilise us. We will meet in court. The name of Barça, this crest, no one tarnishes it. We will take care of it. We will go after them because we have everything to win."
The dispute traces back to comments Pérez made during a press conference on May 12, called to announce Real Madrid's presidential elections, in which he reiterated long-standing accusations against Barcelona over the Negreira case.
"The corruption in the Negreira case is systemic. It is the biggest scandal in history. That we have to listen to the president of the CTA saying these are things that should be forgotten... but how can they be forgotten? We are putting together a 500-page dossier that we are going to send to UEFA — I have already gone to speak with them.
"There is no precedent in the history of world football. How are we going to forget the biggest corruption case there has ever been. Let's see if we are serious and UEFA finally gets involved in this matter, which it will, because it cannot allow the most important football in the world, that of Europe, to be under suspicion of corruption paid for over 20 years."
The timing carries particular weight. Spain's Tax Agency published a report on May 18 concluding there is no evidence that payments made by Barcelona to José María Enríquez Negreira, the former vice-president of Spain's refereeing technical committee, were used to bribe referees or influence La Liga results — a finding Barcelona's legal team will likely cite as central to their case that Pérez's claims were made "with knowledge of their falsehood."
The Negreira case itself remains under judicial investigation in Spain, with Barcelona, former presidents Sandro Rosell and Josep Maria Bartomeu, and Negreira himself among those indicted on charges including corruption and breach of trust — charges Barcelona has consistently denied, maintaining the payments related to legitimate consultancy and scouting reports on referees.
The conciliation demand opens a window for Pérez to apologise or retract before Barcelona escalates to a criminal complaint. Given the personal animosity between the two clubs' leadership — an animosity that has defined much of the past three years of Spanish football's off-field discourse — a swift resolution appears unlikely.