K-Fed -- I Want a Custody Hearing STAT

TMZ has learned that Kevin Federline has asked a judge for an emergency hearing on Thursday to discuss his custody dispute with estranged wife Britney Spears.

A court spokesperson says only K-Fed and his attorney are scheduled to appear before the judge, but adds "anything is possible."

Federline filed papers in November seeking spousal support and sole custody of the couple's children- 5-month-old Jayden James and 17-month-old Sean Preston. As TMZ previously reported, a temporary court order granted the couple joint custody, with Spears having primary physical custody of the boys.

Now, with Spears' recent erratic behavior, coupled with the fact that she's been in and out of rehab twice in the last week, all bets may be off.