I know the broadcast ABC,NBC,CBS etc shows at 10:00 PM show occasional backal nudity with a nipple or two shown on corpses or in medically oriented segments, but suppose they wanted to go topless at 10:00 PM for umm… say a Sweeps Week survey of how hard it is to be a young stripper in L.A.
Other than viewers turning away, who’s to say they can’t? Does the FCC have detailed breast/no breast criteria?
Each network has a “Standards and Practices” office that would review what is planned and determine if within network standards (and standards have changed considerably over the years).
The FCC determines what to do by complaints about it. There are only general guidelines, though a network can be fined if it broadcasts something that FCC determines to be inappropriate. The general rule is that you can get away with more if you show it later at night, and provide a disclaimer.
There’s a fairly substantial body of court cases dealing with the limitations of the power of the FCC to regulate what is broadcast. Without going into too many dull details, the FCC has the power to ban the broadcast of “obscene” material. It does not have the power to ban “indecent” material, but may regulate it by, for example, restricting it to certain hours of the day. As RealityChuck noted, the decisions by the FCC are largely on a case-by-case basis. Check this FCC site for more information on the FCC’s enforcement powers.