The club chief says "the supporters are part of the club but now they have overstepped the mark."
Lazio president Claudio Lotito said he received death threats following the sale of star midfielder Hernanes to Serie A rival Inter.
The Brazil international made the switch for an undisclosed fee at the end of the January transfer window, prompting a backlash from supporters of the Roman club.
"I received between 50 to 70 to 80 telephone calls from pseudo-fans, in which they asked me to leave Lazio and made death threats against me," Lotito told reporters. "I live under escort. The supporters are part of the club but now they have overstepped the mark."
Lotito then explained to the assembled media that his hands were tied over Hernanes' move to San Siro, arguing that he had to cash in on the player in January before losing him for nothing at the end of his contract.
"It was his decision to leave, so what could I do? He had an agreement with Inter. If he had stayed, he would have been unhappy," he said. "He would have stayed here unhappy until June, then gone off to the World Cup, then come back for a few months and left on a free transfer. If you want to leave, you've got to say so."