The Guardia di Finanza (financial police) spent Tuesday morning executing search warrants at the offices of Serie A clubs including AC Milan, Juventus, Lazio and Fiorentina.
Bari, Siena, Palermo, Pescara and Cesena were among the high-profile Serie B clubs probed while police also requisitioned paperwork from Lega Pro clubs including Gubbio and Portogruaro.
A statement published by the Procura di Napoli also confirmed several "foreign clubs" were under investigation, but the office declined to identify them.
The investigation concerns an alleged criminal conspiracy to avoid paying tax to authorities during the transfer of players.
The prosecutors seek to form a "complete reconstruction of the relationship between clubs and players who have, either directly or indirectly, been involved with football agents Alejandro Mazzoni and Alessandro Moggi".
There are currently 12 football agents, including Mazzoni and Moggi, under investigation.
The latter is the son of former Napoli and Juventus administrator Luciano Moggi, who was involved in the 2006 Calciopoli scandal.