Serie A club Siena said in a statement that police had visited their offices as part of investigations being directed by an anti-mafia unit in Naples.
The club said they had suspended two of their players, striker Nicola Ventola and Roberto D'Aversa, who have been named in the investigation.
Siena said they had not been accused of any wrongdoing as a club, adding that players from 11 other clubs were also being investigated.
The club said they had "never had any reason to doubt the motives" of the players but had suspended them from their duties in order to "grant them absolute freedom of action to defend their professional reputation".
Tuscan club Siena are in their first year in Serie A and have secured their top-flight status again for next season.
D'Aversa said he was shocked by the news.
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A source close to the investigation in Naples said five players, including the two Siena squad members and their former goalkeeper Generoso Rossi, were under investigation, adding that phone conversations involving players had been intercepted.
The source said Serie A clubs Chievo, Lecce and Reggina were among those being probed but all said that while their offices had been visited, neither the club nor any of their players had been formally placed under investigation and documents had not been taken away.
Italian soccer was hit by a major gambling and match-fixing scandal in the early 1980s and there have been several smaller cases since.
A number of investigations into Italian soccer are currently underway, focusing on false accounting and suspicion of fraud.