There shall be collected and paid into the Treasury of the United States a fee, prescribed by the Secretary of State by regulation, for the filing of each application for a passport (including the cost of passport issuance and use) and a fee, prescribed by the Secretary of State by regulation, for executing each such application except that the Secretary of State may by regulation authorize State officials or the United States Postal Service to collect and retain the execution fee for each application for a passport accepted by such officials or by that Service. Such fees shall not be refundable, except as the Secretary may by regulation prescribe. No passport fee shall be collected from an officer or employee of the United States proceeding abroad in the discharge of official duties, or from members of his immediate family; from an American seaman who requires a passport in connection with his duties aboard an American flag-vessel; from a widow, widower, child, parent, grandparent, brother, or sister of a deceased member of the Armed Forces proceeding abroad to visit the grave of such member or to attend a funeral or memorial service for such member; or from an individual or individuals abroad, returning to the United States, when the Secretary determines that foregoing the collection of such fee is justified for humanitarian reasons or for law enforcement purposes. No execution fee shall be collected for an application made before a Federal official by a person excused from payment of the passport fee under this section.