The split between Nia Long and Ime Udoka is getting nastier ... the actress is now asking for primary custody of the couple's child -- after she claims the NBA head coach has been failing to support the kid.
Long made the allegation in a court filing in Los Angeles last week ... while requesting a judge give her primary legal and physical custody of their 11-year-old son, Kez.
According to the docs, however, she did ask the judge to allow Udoka a reasonable opportunity to visit their kid to the extent "consistent with the child's best interest.