COVISOC, the regulator for Italian soccer, reported that Serie A champion Inter would not have cleared the annual parameters required for all clubs for the 2005-06 season if it had reported its books accurately.
Inter was awarded the 2005-06 Serie A title when Juventus was stripped of the honor following the Italian match-fixing scandal.
"We are absolutely not considering giving up the 2005-06 title, because it was fairly assigned to us," Inter president Massimo Moratti said. "And that would almost seem like an admission of guilt."
Irregularities were cited for Milan in 2003 and '04.
Also, player transfers between Inter and Milan from 2003-05 are being examined.
Inter released a statement denying it made any false reports and Moratti called the investigation "absurd."
"I pay billions every day," Moratti said. "I normally don't make any bookkeeping errors, although it is true that the worth of players in this market is difficult to understand. A player that is worth five today could be worth 12 within a month, and then maybe nothing."