What about nonprofit underwriters? Do all the same rules apply?
PBS national guidelines do not distinguish between for-profit and non-profit underwriters. The federal statute governing noncommercial broadcasts, however, does make a distinction, and some stations have relied on the legal definition of “advertisement,” as noted above, to allow more flexibility for nonprofit underwriting messages -- as long as that message is not in support of an issue or political candidate. But more often than not, this is not (nor should be) a simple decision for stations, as the following history and additional considerations come into play:
There are a wide variety of nonprofit groups (including hospitals, educational institutions, concerts, theatre performances, art galleries), traditional charities such as Red Cross, governmental entities such as city or county agencies, and advocacy groups such as Sierra Club, which value public television as a media and marketing partner. The rules with respect to these groups used to be relatively straightforward, because the definition of an advertisement contained in the Communications Act applies only to those "engaged in such offering for profit." That allowed public stations to charge a nonprofit for announcements that promoted the nonprofit or its activities.
The picture became more complicated in 2002 when the IRS adopted a different definition of "advertising." The IRS definition is not limited to for-profits, as the IRS is not convinced that the promotion of another nonprofit is 'related' to a public television station’s education purpose. Thus, while promoting a nonprofit’s activities on-air is allowed (as long as that message is not in support of an issue or political candidate), any revenue derived from doing so may be subject to Unrelated Business Income Tax (UBIT). One solution is to make nonprofits comply with the same underwriting principles with which commercial underwriters must comply. So long as an announcement merely "identifies" the nonprofit, UBIT will not apply. Like PBS then, many stations choose to take this approach, for tax reasons and to keep their on-air environment as non-commercial as possible.
Finally, FCC policy prohibits public television stations from fundraising on behalf of nonprofits or other entities when it involves the suspension of regular programming. (e.g., charity telethons). The general idea is that, when public broadcasters suspend regular programming to appeal to the public for money, it has to be for the benefit of the station itself, as in the usual pledge or auction programming. The FCC has granted waivers only in limited and extraordinary circumstances, including 9/11, Hurricane Katrina, and Hurricane Sandy.