Police arrived at Italy's pre-Euro 2012 training camp in Coverciano, Florence, this morning to question former Genoa and Juventus defender Domenico Criscito, who is now a player at Zenit St Petersburg in connection with a match-fixing probe.
Lazio captain Stefano Mauri and former Genoa midfielder Omar Milanetto have been arrested by police.
Mauri and Milanetto have been held over allegations of "criminal association and sporting fraud", according to Italian news agency ANSA.
Officers are searching more than 19 homes in Italy and abroad, including those of coaches and players of clubs in Serie A, Serie B and lower divisions.
Juventus coach Antonio Conte, who just led the club to the Serie A title in his first season in charge, is among numerous individuals being questioned by police.
Today's operation is part of an investigation called "Last Bet" carried out by prosecutors in Cremona which focuses on 33 games over the past two seasons, the majority of which were in Serie B.
Earlier this month, the Italian Football Federation released a comprehensive 48-page list naming 22 clubs along with 61 individuals that have been reported to the football authorities in connection with a match-fixing ring and betting investigation.
Seventeen people were arrested by Italian police last year, including Atalanta captain Cristiano Doni.
Atalanta, who had been promoted to Serie A at the end of the 2010-11 season, began the recently completed campaign with a six-point deduction as punishment for match-fixing.
Doni was banned from football for three and a half years by the FIGC's disciplinary committee.