Kevin Federline's lawyers want Britney Spears to pay some of her former husband's legal expenses in their divorce case, court documents show.
Spears filed for divorce from Federline last November
Mark Vincent Kaplan says his client has "no net income" after various expenses, and that Ms Spears is "clearly the monied party" in the dispute.
According to legal documents filed in Los Angeles, the pop star's average monthly income is $737,868 (£365,966).
The couple married in October 2004 and filed for divorce last November.
Their separation was finalised in July, but Mr Federline's lawyers argue that Ms Spears should pay $50,000 (£24,788) towards his legal expenses.
Ms Spears' lawyers were not available for comment about the move.
Since their divorce, the couple have been battling over custody of their two young sons.
Ms Spears, 25, and Mr Federline, 29, have shared joint custody of 22-month-old Sean Preston and 10-month-old Jayden James, since February.
Since then, Ms Spears has spent a spell in rehab following months of high-profile partying and a dramatic hair cut.
Mr Federline is seeking additional custody because the two boys are "isolated from risks" when they are with him, according to his lawyer.
A hearing on the custody modification request is set for 17 September, but lawyers for Ms Spears have asked that it be postponed until November.