Narnia
Banned
This really is ASB. For local stations, advertising revenue is what keeps them on the air and it is their only real source of income. Take that away and every local station closes up shop. You also have a small constitutional issue in the US as commercial speech, while not as protected as some, still has some protection. I'm not sure an outright ban would be viewed as constitutional, though, to be fair, bans on cigarette ads on TV and other media have been upheld.
On the other hand, this would immensely improve the quality of US political campaigns and dramatically lower their costs, as broadcast advertising is easily half or more of the budget of a major campaign and a source of constant irritation come election time.
That's why I figured that the only way for this could work would be for the country in question to adopt a Soviet-style command economy. This just won't work in a free market. Maybe a few premium channels will survive, but that way TV will be something only the rich could have. Also, the OP never said that this was in the USA. It could be in Canada, China, Iran or any other country.