The NBPA's executive committee voted 8-0 for Derek Fisher to step down as president.
"The Executive Committee based its decision on numerous instances over the past six months, where Fisher engaged in conduct detrimental to the union, including acting in contravention of the players' best interests, during collective bargaining, declining to follow the NBPA Constitution, and failing to uphold the duties of the Union President," the statement said.
Fisher spoke briefly to reporters on Friday.
"The quickest, most efficient way to say it is to say that I do and I've always taken my job as president of the players' association very, very seriously."
Fisher and Billy Hunter have been at odds since the middle of the lockout.