I was on a leave of absence. Do I still owe dues/service charges?

YES – Every Flight Attendant owes dues for the first three months (90 days) of any unpaid leave of absence except military and involuntary furlough.
NOTE: AFA-CWA does not consider the leave status to be effective until such time that you are no longer receiving sick bank and/or vacation. In other words, at the time you enter the non-pay status, the 90-day financial obligation for dues while on leave begins.