Barcelona say they have offered "full collaboration" to a police investigation following a raid on the club's offices.
In a statement tweeted on Monday, Los Mossos d'Esquadra confirmed "several searches are being carried out" at Barca's club premises by its unit dedicated to the investigation of economic crimes.
A club statement read: "Regarding the entry and search by the Catalan Police force this morning at the Camp Nou offices by order of the Instructing Court number 13 in Barcelona, which is in charge of the case relating to the contacting of monitoring services on social networks, FC Barcelona have offered up their full collaboration to the legal and police authorities to help make clear facts which are subject to investigation.
"The information and documentation requested by the judicial police force relate strictly to the facts relative to this case.
"FC Barcelona express its utmost respect for the judicial process in place and for the principle of presumed innocence for the people affected within the remit of this investigation."
According to the EFE news agency, former Barca president Josep Maria Bartomeu has been taken into custody as part of the probe, along with the club's current CEO Oscar Grau.
Barca's head of legal services Roman Gomez Ponti and former director Jaume Masferrer were also arrested, EFE said.
It is thought the investigation surrounds the "Barcagate" scandal, where it was alleged Barcelona had paid social media company 13 Ventures to smear club greats such as Lionel Messi, Pep Guardiola, Xavi, Gerard Pique and ex-president Joan Laporta during Bartomeu's leadership.
In July 2020, Barca's offices were searched by Los Mossos in relation to claims, although the club hired Price Waterhouse Coopers to investigate the matter and the global auditing firm found in their favour.
However, Emili Rousaud, Enrique Tombas, Silvio Elias, Josep Pont, Maria Teixidor, Noelia Ronero and Jordi Calsamiglia resigned as board members as a result of the damaging fallout.
Bartomeu stepped down as Barca president in October ahead of a vote of no confidence in his leadership, a move that had followed a close season of turmoil in which Messi attempted to leave Camp Nou.
Elections to choose his successor are scheduled to take place on Sunday amid another turbulent episode at Barca, with Laporta the favourite to return for a second stint in charge.