Italy goalkeeper Gianluigi Buffon and World Cup referee Massimo De Santis were among dozens of people reportedly implicated.
"It is terrible," Silvio Berlusconi, the outgoing Italian prime minister whose business empire includes AC Milan, said.
The football federation said on Friday, Carabinieri paramilitary police searched its Rome offices but refused to give details.
The Ansa news agency said police seized documents related to a probe by Naples prosecutors concerning the 2004-2005 season.
Ansa said the association of Italian referees was also being searched in connection with allegations that the director-general of Juventus tried to influence the choice of match officials.
The entire Juventus board resigned on Thursday, including Antonio Giraudo, the managing director, and Luciano Moggi, general director, who is under investigation for allegedly trying to influence referee assignments.
Naples prosecutor Giovandomenico Lepore said in that city that investigators were looking into 20 matches from the 2004-2005 season - 19 in Serie A, and one in Serie B.
Another Naples prosecutor, Giuseppe Narducci, said four Serie A clubs were being probed - Juventus, Lazio, AC Milan and Fiorentina.
At the end of the 1979-80 season, Italy was shaken by a match-fixing scandal that led to AC Milan and Lazio being demoted to Serie B.
Fiorentina said in a statement on Friday that the Della Valle family, which owns the team, was certain of its "correct conduct".
Lepore said 41 people had been ordered to appear for questioning for suspected criminal association or sports fraud.
Ansa said Moggi and Giraudo were also being investigated for possible involvement in kidnapping in connection with a Reggina victory over Juventus in November 2004.
Three referees were allegedly locked in a dressing room by the two Juve officials as punishment for not having assured victory for the Turin club, the report said.
Prosecutors did not publicly name any people in connection with specific crimes.
Club officials, federation officials, officials who assign referees to matches, referees and a journalist are among those under investigation, Lepore said, adding that because the probe was still in progress he could not give specific details.
On Thursday, the entire board of
Italy's Juventus club resigned
Without citing sources, ANSA reported from Naples that De Santis, an Italian referee assigned to the June 9-July World Cup in Germany, was among those ordered for questioning.
In another probe, Parma prosecutor Pietro Errede told state TV that investigators there were looking into a suspected betting scandal involving allegedly fixed matches.
Among the names of players cited in Italian news reports on Friday about the betting probe was that of Buffon, the Juventus and Italy goalkeeper.
Any involvement could cost Buffon a spot on Italy's World Cup team, which is to be finalised by Monday.
Turin newspaper La Stampa reported that Buffon was alleged to have bet hundreds of thousands of euros. Players are banned from any kind of betting on Italian soccer league matches.
Juventus declined to comment.
Buffon signed T-shirts and hats for fans in Turin after training but declined to answer a reporter's question about the scandal.
"Who ever did wrong must pay," AS Roma star Francesco Totti told ANSA. "We need to clean the whole thing up. As for names, I don't know them and I don't want to know.".