League spokesman Tim Frank confirmed the fine Friday before the Nets played the New York Knicks at the Prudential Center.
NBA rules prohibit team personnel from having contact with players who are not yet draft eligible.
The NBA's investigation, first reported by CBSSports.com, was triggered by a video showing Jay-Z visiting with various Kentucky players in their locker room at Prudential Center in Newark, N.J., after the Wildcats' quarterfinal victory over North Carolina.
Though the circumstances of the visit seemed harmless enough, with Kentucky players clearly more excited about meeting a world-famous rap mogul as opposed to a part-time NBA team executive, Nets officials were expecting a fine based on what happened to Boston Celtics general manager Danny Ainge in 2007.
Boston was fined $30,000 that year for "excessive contact with the family" after Ainge was spotted sitting next to Kevin Durant's mother at the Big 12 tournament.
Marc Stein is a senior NBA writer for ESPN.com. Information from The Associated Press was used in this report.