Emails from the Hawks tried to lure potential ticket purchasers by suggesting the signings of Los Angles Clippers guard Chris Paul and Lakers center Dwight Howard were imminent.
"The buzz around our offseason is more than heating up," the Hawks email said. "With massive cap space, 4 draft picks, and free agency rapidly approaching, we sit in the best position in the NBA."
"Player interest is skyrocketing as the possibilities of landing Chris Paul & Dwight Howard become more and more of a reality. This is your opportunity to get on board before its [sic] too late. Once we solidify our signings there will be no seats left."
The size of the fines and the other two teams have not been made public.
"The conduct at issue involved statements by a team employee to the media, a team email to prospective season ticket purchasers, and articles posted online on a team website, each related to players who are currently under contract to other teams but will become free agents this summer," a memo said.
A statement from the Hawks said team officials "fully understand and respect the NBA's decision."
The NBA constitution says tampering can be punished by suspension of the offending person, prohibition of the team from hiring the person being tampered with, forfeiture of draft picks and team fines up to $5 million.
It defines tampering as:
"any person affiliated with an NBA team directly or indirectly (i) entice, induce, or persuade, or attempt to entice, induce or persuade, any player, coach, GM or other person under contract to any other NBA team to enter into negotiations for or relating to that person's services or to negotiate or contract for such services, or (ii) otherwise interfere with the employment relationship between that employee and the other NBA team."