Three top-ranking members of the Italian referees association (AIA) have received packages filled with bullets, according to the body's president Marcello Nicchi.
Nicchi claimed he, vice-president Narciso Pisacreta and referee selector Nicola Rizzoli - who officiated the 2014 World Cup final - were all sent the parcels in the mail.
In December, an aggrieved group of Biancocelesti supporters also initiated legal action against match officials Piero Giacomelli and Marco Di Bello over perceived errors in a 3-1 loss to Torino.
"Yesterday Di Bello managed the Milan derby very well, yet he and [Giacomelli] will have to appear before the justice of the peace because of supposed errors," Nicchi said on Thursday.
"Tell me, if Lionel Messi or Cristiano Ronaldo or a Serie A player misses a chance, are they up in court the next week? This is scandalous.
"How can we send our referees on to the pitch when, if they happen to make a mistake, they might be subjected to this same fate?"
Scudetto contenders Napoli took to social media to condemn the intimidation of the AIA staff members.
"Footballers and referees are the sport's key players," the club wrote on Twitter.
"Sending bullets to referees in an attempt to undermine the integrity of such a wonderful, popular sport is a truly cowardly act. Napoli is shocked by these reports."
Football is a game that belongs to everyone. Footballers and referees are the sport's key players. Sending bullets to referees in an attempt to undermine the integrity of such a wonderful, popular sport is a truly cowardly act. Napoli is shocked by these reports.— Official SSC Napoli (@en_sscnapoli) April 5, 2018