I am on a voluntary furlough. Do I still owe dues?

Yes. In accordance with the AFA-CWA Constitution & Bylaws every flight attendant on a leave of absence owes dues for the first three (3) months of their leave of absence AFTER their compensation from their airline ends. Those flight attendants on a military leave or involuntary furlough do not owe this amount.
This is part of the AFA-CWA Constitution & Bylaws: “Article XI A.6. Payment of dues shall be required of all members that are on active status during a month or any portion thereof. After the first ninety (90) days of removal from service and no longer receiving compensation through a carrier for disability leave, payment of dues shall not be required.”   The Constitution and Bylaws is written and approved by the AFA Board of Directors which consists of all LEC Presidents, including yours.