"We voiced with the Commissioner today our view on the inappropriate comments by Knicks President Phil Jackson," Roberts said in a statement. "If players under contract cannot, under threat of league discipline, speak openly about their desire to be employed elsewhere, we expect management to adhere to the same standards. The door swings both ways when it comes to demonstrating loyalty and respect."
Jackson told reporters Friday that he will continue to explore trade options for Carmelo Anthony, saying the All-Star forward "would be better off somewhere else."
Anthony, 32, was the subject of rampant trade speculation throughout the season, which at one point prompted the 10-time All-Star to tell Jackson that he wanted to remain with the Knicks and would not waive his no-trade clause.
Roberts' statement refers to a league rule that mandates players be fined for publicly requesting trades. A player can express a desire for a change of scenery privately, but a public statement is automatically subject to a fine.
Anthony is an NBPA vice president. The Knicks did not immediately respond to Roberts' statement.
Anthony said Wednesday that he would "love" to return to the Knicks but wanted the team to make a commitment to winning immediately. He has said in the past that if the Knicks presented him with a trade proposal, he would listen.
Jackson's Friday conference focused on the situation with Anthony three days after the Knicks finished the season 31-51 for their fourth straight losing season.
"We've not been able to win with [Anthony] on the court at this time," Jackson said Friday. "I think the direction with our team is that he's a player that would be better off somewhere else and using his talent somewhere where he can win or chase that championship."
ESPN's Ian Begley and The Associated Press contributed to this report.