The Fairness Doctrine.
In Red Lion Broadcasting v. the FCC, the Supreme Court upheld the Fairness Doctrine, that is, the doctrine that requires news organs to present a fair and balanced view of the news.
Since broadcasters get licenses to broadcast from the FCC, they have to abide by FCC regulations.
Fairness Doctrines, in the eyes of SCOTUS, do not violate the 1st Amendment due to the important role that broadcasters play and scarce options available.