Attorney Mark Vincent Kaplan said in an Aug. 26 declaration that Federline has "no net income" after various expenses, and that his spousal support of $20,000 a month ends in November. Spears, meanwhile, brings in an average monthly income of $737,868.
Spears is "clearly the 'monied party' " in the dispute and should pay $50,000 for Federline's litigation expenses, Kaplan argued.
An after-hours message left Thursday with Spears' attorney was not immediately returned.
Spears married Federline in October 2004, eight months after her first marriage to childhood friend Jason Alexander was annulled. She cited irreconcilable differences when she filed for divorce from Federline on Nov. 7, 2006.
Since February, Spears, 25, and Federline, 29, have shared custody of their sons, 23-month-old Sean Preston and 11-month-old Jayden James.
A hearing is scheduled for Sept. 17, but an attorney for Spears has requested a continuance until November.