National Park Service
(NPS). The federal agency requires a permit from a park manager for any letterboxes (or geocaches) planted in any of the parks under its jurisdiction. They have been known to remove letterboxes that have been planted in their parks without a permit, and even issue citations to offenders. (See confiscated letterbox.) A very few National Parks have allowed letterboxes to be planted within their boundaries, so you should contact the park rangers to obtain a permit before planting any box in a National Park. Note: National Forests are under the jurisdiction of a different branch of the federal government, and thus have different rules regarding letterboxing; generally, National Forests are more amenable to the activity.