Lazio president Claudio Lotito has alleged Juventus' pursuit of Keita Balde "practically qualifies as a crime".
Lotito claims the Turin giants offered €15 million for the attacker - half the amount put forward by AC Milan, West Ham and Napoli, all of whom were turned down by Keita.
Keita did not feature in Lazio's Supercoppa Italiana win over Juve last weekend but his agent refuted reports his client had refused to play to try and force through a move.
The Senegal international has one year remaining on his contract but Lotito stressed that does not give Juve free rein to table miserly bids.
"First things first, it's not true that we have not proposed a new contract to Keita," Lotito told La Gazzetta dello Sport.
"We met twice with his agent Roberto Calenda and Keita's brother was present too. We offered him the same wages as Miroslav Klose, the highest-paid player under my tenure. The response was that he wanted to leave Lazio.
"There were three formal offers, all of them I can prove with documentation. Milan would have given us €35m, West Ham €32m and Napoli €30m.
"Keita and his agent replied that they were not interested in any of the three, that the destination they wanted was Juventus. The player confirmed it to me in the pre-season training camp.
"Juve consider €15m to be a suitable offer, but I cannot sell a player for half of the lowest other offer I received. If I got proposals worth €30m, why should I sell him for half that?
"You tell me his contract is running down and I risk losing him for nothing if I don't accept? Well I say that is extortion and practically qualifies as a crime.
"We will evaluate taking legal action. A contract must be respected and not just if a player doesn't get game time. It's also false to say that he was dropped because of a club diktat, as it was purely Simone Inzaghi's choice.
"They tell me that in the locker room the player confessed he didn't feel up to playing, then seemed below par in the training session. What a coincidence, he was going to play against Juve...
"Inzaghi will decide whether to use Keita or not this season. As for his contract running down, zero patience. It is more important to respect the rules."