Catalan police say they have made four arrests after searching the offices of Spanish side Barcelona.
The identity of those involved have not yet been confirmed by police, who said their investigation is continuing.
The police operation was conducted on Monday after an investigation into financial issues at Barcelona.
Those issues are thought to be related to the 'Barcagate' scandal in 2020 when the club denied hiring a firm to attack their own players on social media.
The club's presidential elections take place on Sunday after their previous president, Josep Maria Bartomeu, announced his resignation in October.
According to Spanish media reports, Bartomeu is among those arrested - although police have not confirmed this.
In a statement, Barcelona said the police searches related 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 club said.
"The information and documentation requested by the judicial police force relate strictly to the facts relative to this case.
"FC Barcelona expresses 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."
Police said they also searched four other properties as part of their investigation, "which has been going on for almost a year".
Andy West, Barcelona-based football writer
The idea that one of the world's most prestigious football clubs would hire a social media company to run an undercover smear campaign against its own players and their families seems far-fetched beyond belief.
But considering the battering that Barca's reputation took under former president Josep Maria Bartomeu, it's perhaps almost a logical development.
This story has been rumbling around for more than a year, and was one of the sources of a deep rift between the old board and the playing squad that led captain Lionel Messi to launch an aborted attempt to quit the Nou Camp last summer, and ultimately led to Bartomeu's overdue resignation.
Perhaps the saddest thing is that nobody around Barcelona would be particularly surprised if the accusations proved to be accurate.
The timing of Monday's police action is ironic, coming just a few days before the disgraced Bartomeu's successor is anointed in the presidential elections.
Whoever wins that vote of the club's members, Monday's news makes it painfully clear that, in addition to rebuilding a world-class team on the field of play, the task of restoring Barca's ruined reputation for being 'more than a club' is equally enormous.
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