Dont public TV stations already air commercials?
No. Although in 1981 Congress passed a law allowing public TV stations to provide certain revenue-generating services, the law specifically prohibits them from broadcasting advertisements. They are allowed, however, to acknowledge contributions or underwriting donations from for-profit entities with announcements naming and generally describing the entities. The Commission has rules that distinguish such underwriting announcements from advertising aired on commercial TV. For additional information, see In the Matter of Commission Policy Concerning the Noncommercial Nature of Educational Broadcasting.
