The members of her management team quit in the past couple of weeks amid reports of the "Hairspray" and "What a Girl Wants" star's erratic behavior.
TMZ said the three unnamed representatives dropped Bynes as a client after she stopped meeting with them and taking their calls.
Bynes, 26, has been making headlines for months in connection with several alleged motor-vehicle violations and reported substance abuse.
The actress began her career on TV's "The Amanda Show" and "What I Like About You."
Swim Week Miami Beach 2014 [PHOTOS]