The Anti-Defamation League is refusing to accept Kyrie Irving's donation ... with its CEO saying in a statement Thursday the org. is giving back the $500K that the Nets star donated this week.

Jonathan Greenblatt made the announcement on his Twitter page -- just minutes after Brooklyn suspended the point guard for at least five games.

In his statement, Greenblatt said that after Irving refused to specifically apologize for tweeting out a link to a film that contained antisemitic rhetoric despite having multiple opportunities to do so ... the ADL "cannot in good conscience accept his donation."

"We were optimistic," Greenblatt said, "but after watching the debacle of a press conference, it’s clear that Kyrie feels no accountability for his actions."

Irving initially made the donation on Wednesday evening ... with the Nets saying they'd match his pledge. A statement came attached to the announcement of the contribution, with Irving appearing to express remorse for his tweet.